gcc/libstdc++-v3/include/ext/stl_rope.h

// SGI's rope implementation -*- C++ -*-

// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

/*
 * Copyright (c) 1997-1998
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/* NOTE: This is an internal header file, included by other STL headers.
 *   You should not attempt to use it directly.
 */

// rope<_CharT,_Alloc> is a sequence of _CharT.
// Ropes appear to be mutable, but update operations
// really copy enough of the data structure to leave the original
// valid.  Thus ropes can be logically copied by just copying
// a pointer value.

#ifndef __SGI_STL_INTERNAL_ROPE_H
# define __SGI_STL_INTERNAL_ROPE_H

# ifdef __GC
#   define __GC_CONST const
# else
#   include <bits/stl_threads.h>
#   define __GC_CONST   // constant except for deallocation
# endif
# ifdef __STL_SGI_THREADS
#    include <mutex.h>
# endif

namespace std
{

// The _S_eos function is used for those functions that
// convert to/from C-like strings to detect the end of the string.

// The end-of-C-string character.
// This is what the draft standard says it should be.
template <class _CharT>
inline _CharT _S_eos(_CharT*) { return _CharT(); }

// Test for basic character types.
// For basic character types leaves having a trailing eos.
template <class _CharT>
inline bool _S_is_basic_char_type(_CharT*) { return false; }
template <class _CharT>
inline bool _S_is_one_byte_char_type(_CharT*) { return false; }

inline bool _S_is_basic_char_type(char*) { return true; }
inline bool _S_is_one_byte_char_type(char*) { return true; }
inline bool _S_is_basic_char_type(wchar_t*) { return true; }

// Store an eos iff _CharT is a basic character type.
// Do not reference _S_eos if it isn't.
template <class _CharT>
inline void _S_cond_store_eos(_CharT&) {}

inline void _S_cond_store_eos(char& __c) { __c = 0; }
inline void _S_cond_store_eos(wchar_t& __c) { __c = 0; }

// char_producers are logically functions that generate a section of
// a string.  These can be convereted to ropes.  The resulting rope
// invokes the char_producer on demand.  This allows, for example,
// files to be viewed as ropes without reading the entire file.
template <class _CharT>
class char_producer {
    public:
        virtual ~char_producer() {};
        virtual void operator()(size_t __start_pos, size_t __len, 
                                _CharT* __buffer) = 0;
        // Buffer should really be an arbitrary output iterator.
        // That way we could flatten directly into an ostream, etc.
        // This is thoroughly impossible, since iterator types don't
        // have runtime descriptions.
};

// Sequence buffers:
//
// Sequence must provide an append operation that appends an
// array to the sequence.  Sequence buffers are useful only if
// appending an entire array is cheaper than appending element by element.
// This is true for many string representations.
// This should  perhaps inherit from ostream<sequence::value_type>
// and be implemented correspondingly, so that they can be used
// for formatted.  For the sake of portability, we don't do this yet.
//
// For now, sequence buffers behave as output iterators.  But they also
// behave a little like basic_ostringstream<sequence::value_type> and a
// little like containers.

template<class _Sequence, size_t _Buf_sz = 100>
class sequence_buffer : public output_iterator {
    public:
        typedef typename _Sequence::value_type value_type;
    protected:
        _Sequence* _M_prefix;
        value_type _M_buffer[_Buf_sz];
        size_t     _M_buf_count;
    public:
        void flush() {
            _M_prefix->append(_M_buffer, _M_buffer + _M_buf_count);
            _M_buf_count = 0;
        }
        ~sequence_buffer() { flush(); }
        sequence_buffer() : _M_prefix(0), _M_buf_count(0) {}
        sequence_buffer(const sequence_buffer& __x) {
            _M_prefix = __x._M_prefix;
            _M_buf_count = __x._M_buf_count;
            copy(__x._M_buffer, __x._M_buffer + __x._M_buf_count, _M_buffer);
        }
        sequence_buffer(sequence_buffer& __x) {
            __x.flush();
            _M_prefix = __x._M_prefix;
            _M_buf_count = 0;
        }
        sequence_buffer(_Sequence& __s) : _M_prefix(&__s), _M_buf_count(0) {}
        sequence_buffer& operator= (sequence_buffer& __x) {
            __x.flush();
            _M_prefix = __x._M_prefix;
            _M_buf_count = 0;
            return *this;
        }
        sequence_buffer& operator= (const sequence_buffer& __x) {
            _M_prefix = __x._M_prefix;
            _M_buf_count = __x._M_buf_count;
            copy(__x._M_buffer, __x._M_buffer + __x._M_buf_count, _M_buffer);
            return *this;
        }
        void push_back(value_type __x)
        {
            if (_M_buf_count < _Buf_sz) {
                _M_buffer[_M_buf_count] = __x;
                ++_M_buf_count;
            } else {
                flush();
                _M_buffer[0] = __x;
                _M_buf_count = 1;
            }
        }
        void append(value_type* __s, size_t __len)
        {
            if (__len + _M_buf_count <= _Buf_sz) {
                size_t __i = _M_buf_count;
                size_t __j = 0;
                for (; __j < __len; __i++, __j++) {
                    _M_buffer[__i] = __s[__j];
                }
                _M_buf_count += __len;
            } else if (0 == _M_buf_count) {
                _M_prefix->append(__s, __s + __len);
            } else {
                flush();
                append(__s, __len);
            }
        }
        sequence_buffer& write(value_type* __s, size_t __len)
        {
            append(__s, __len);
            return *this;
        }
        sequence_buffer& put(value_type __x)
        {
            push_back(__x);
            return *this;
        }
        sequence_buffer& operator=(const value_type& __rhs)
        {
            push_back(__rhs);
            return *this;
        }
        sequence_buffer& operator*() { return *this; }
        sequence_buffer& operator++() { return *this; }
        sequence_buffer& operator++(int) { return *this; }
};

// The following should be treated as private, at least for now.
template<class _CharT>
class _Rope_char_consumer {
    public:
        // If we had member templates, these should not be virtual.
        // For now we need to use run-time parametrization where
        // compile-time would do.  Hence this should all be private
        // for now.
        // The symmetry with char_producer is accidental and temporary.
        virtual ~_Rope_char_consumer() {};
        virtual bool operator()(const _CharT* __buffer, size_t __len) = 0;
};

// First a lot of forward declarations.  The standard seems to require
// much stricter "declaration before use" than many of the implementations
// that preceded it.
template<class _CharT, class _Alloc=allocator<_CharT> > class rope;
template<class _CharT, class _Alloc> struct _Rope_RopeConcatenation;
template<class _CharT, class _Alloc> struct _Rope_RopeLeaf;
template<class _CharT, class _Alloc> struct _Rope_RopeFunction;
template<class _CharT, class _Alloc> struct _Rope_RopeSubstring;
template<class _CharT, class _Alloc> class _Rope_iterator;
template<class _CharT, class _Alloc> class _Rope_const_iterator;
template<class _CharT, class _Alloc> class _Rope_char_ref_proxy;
template<class _CharT, class _Alloc> class _Rope_char_ptr_proxy;

template<class _CharT, class _Alloc>
bool operator== (const _Rope_char_ptr_proxy<_CharT,_Alloc>& __x,
                 const _Rope_char_ptr_proxy<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
_Rope_const_iterator<_CharT,_Alloc> operator-
        (const _Rope_const_iterator<_CharT,_Alloc>& __x,
         ptrdiff_t __n);

template<class _CharT, class _Alloc>
_Rope_const_iterator<_CharT,_Alloc> operator+
        (const _Rope_const_iterator<_CharT,_Alloc>& __x,
         ptrdiff_t __n);

template<class _CharT, class _Alloc>
_Rope_const_iterator<_CharT,_Alloc> operator+
        (ptrdiff_t __n,
         const _Rope_const_iterator<_CharT,_Alloc>& __x);

template<class _CharT, class _Alloc>
bool operator== 
        (const _Rope_const_iterator<_CharT,_Alloc>& __x,
         const _Rope_const_iterator<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
bool operator< 
        (const _Rope_const_iterator<_CharT,_Alloc>& __x,
         const _Rope_const_iterator<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
ptrdiff_t operator- 
        (const _Rope_const_iterator<_CharT,_Alloc>& __x,
         const _Rope_const_iterator<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
_Rope_iterator<_CharT,_Alloc> operator-
        (const _Rope_iterator<_CharT,_Alloc>& __x,
         ptrdiff_t __n);

template<class _CharT, class _Alloc>
_Rope_iterator<_CharT,_Alloc> operator+
        (const _Rope_iterator<_CharT,_Alloc>& __x,
         ptrdiff_t __n);

template<class _CharT, class _Alloc>
_Rope_iterator<_CharT,_Alloc> operator+
        (ptrdiff_t __n,
         const _Rope_iterator<_CharT,_Alloc>& __x);

template<class _CharT, class _Alloc>
bool operator== 
        (const _Rope_iterator<_CharT,_Alloc>& __x,
         const _Rope_iterator<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
bool operator< 
        (const _Rope_iterator<_CharT,_Alloc>& __x,
         const _Rope_iterator<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
ptrdiff_t operator- 
        (const _Rope_iterator<_CharT,_Alloc>& __x,
         const _Rope_iterator<_CharT,_Alloc>& __y);

template<class _CharT, class _Alloc>
rope<_CharT,_Alloc> operator+ (const rope<_CharT,_Alloc>& __left,
                               const rope<_CharT,_Alloc>& __right);
        
template<class _CharT, class _Alloc>
rope<_CharT,_Alloc> operator+ (const rope<_CharT,_Alloc>& __left,
                               const _CharT* __right);
        
template<class _CharT, class _Alloc>
rope<_CharT,_Alloc> operator+ (const rope<_CharT,_Alloc>& __left,
                               _CharT __right);
        
// Some helpers, so we can use power on ropes.
// See below for why this isn't local to the implementation.

// This uses a nonstandard refcount convention.
// The result has refcount 0.
template<class _CharT, class _Alloc>
struct _Rope_Concat_fn
       : public binary_function<rope<_CharT,_Alloc>, rope<_CharT,_Alloc>,
                                     rope<_CharT,_Alloc> > {
        rope<_CharT,_Alloc> operator() (const rope<_CharT,_Alloc>& __x,
                                const rope<_CharT,_Alloc>& __y) {
                    return __x + __y;
        }
};

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>
identity_element(_Rope_Concat_fn<_CharT, _Alloc>)
{
    return rope<_CharT,_Alloc>();
}


//
// What follows should really be local to rope.  Unfortunately,
// that doesn't work, since it makes it impossible to define generic
// equality on rope iterators.  According to the draft standard, the
// template parameters for such an equality operator cannot be inferred
// from the occurence of a member class as a parameter.
// (SGI compilers in fact allow this, but the __result wouldn't be
// portable.)
// Similarly, some of the static member functions are member functions
// only to avoid polluting the global namespace, and to circumvent
// restrictions on type inference for template functions.
//

//
// The internal data structure for representing a rope.  This is
// private to the implementation.  A rope is really just a pointer
// to one of these.
//
// A few basic functions for manipulating this data structure
// are members of _RopeRep.  Most of the more complex algorithms
// are implemented as rope members.
//
// Some of the static member functions of _RopeRep have identically
// named functions in rope that simply invoke the _RopeRep versions.
//
// A macro to introduce various allocation and deallocation functions
// These need to be defined differently depending on whether or not
// we are using standard conforming allocators, and whether the allocator
// instances have real state.  Thus this macro is invoked repeatedly
// with different definitions of __ROPE_DEFINE_ALLOC.
// __ROPE_DEFINE_ALLOC(type,name) defines 
//   type * name_allocate(size_t) and
//   void name_deallocate(tipe *, size_t)
// Both functions may or may not be static.

#define __ROPE_DEFINE_ALLOCS(__a) \
        __ROPE_DEFINE_ALLOC(_CharT,_Data) /* character data */ \
        typedef _Rope_RopeConcatenation<_CharT,__a> __C; \
        __ROPE_DEFINE_ALLOC(__C,_C) \
        typedef _Rope_RopeLeaf<_CharT,__a> __L; \
        __ROPE_DEFINE_ALLOC(__L,_L) \
        typedef _Rope_RopeFunction<_CharT,__a> __F; \
        __ROPE_DEFINE_ALLOC(__F,_F) \
        typedef _Rope_RopeSubstring<_CharT,__a> __S; \
        __ROPE_DEFINE_ALLOC(__S,_S)

//  Internal rope nodes potentially store a copy of the allocator
//  instance used to allocate them.  This is mostly redundant.
//  But the alternative would be to pass allocator instances around
//  in some form to nearly all internal functions, since any pointer
//  assignment may result in a zero reference count and thus require
//  deallocation.
//  The _Rope_rep_base class encapsulates
//  the differences between SGI-style allocators and standard-conforming
//  allocators.

#define __STATIC_IF_SGI_ALLOC  /* not static */

// Base class for ordinary allocators.
template <class _CharT, class _Allocator, bool _IsStatic>
class _Rope_rep_alloc_base {
public:
  typedef typename _Alloc_traits<_CharT,_Allocator>::allocator_type
          allocator_type;
  allocator_type get_allocator() const { return _M_data_allocator; }
  _Rope_rep_alloc_base(size_t __size, const allocator_type& __a)
        : _M_size(__size), _M_data_allocator(__a) {}
  size_t _M_size;       // This is here only to avoid wasting space
                // for an otherwise empty base class.

  
protected:
    allocator_type _M_data_allocator;

# define __ROPE_DEFINE_ALLOC(_Tp, __name) \
        typedef typename \
          _Alloc_traits<_Tp,_Allocator>::allocator_type __name##Allocator; \
        /*static*/ _Tp * __name##_allocate(size_t __n) \
          { return __name##Allocator(_M_data_allocator).allocate(__n); } \
        void __name##_deallocate(_Tp* __p, size_t __n) \
          { __name##Allocator(_M_data_allocator).deallocate(__p, __n); }
  __ROPE_DEFINE_ALLOCS(_Allocator);
# undef __ROPE_DEFINE_ALLOC
};

// Specialization for allocators that have the property that we don't
//  actually have to store an allocator object.  
template <class _CharT, class _Allocator>
class _Rope_rep_alloc_base<_CharT,_Allocator,true> {
public:
  typedef typename _Alloc_traits<_CharT,_Allocator>::allocator_type
          allocator_type;
  allocator_type get_allocator() const { return allocator_type(); }
  _Rope_rep_alloc_base(size_t __size, const allocator_type&)
                : _M_size(__size) {}
  size_t _M_size;
  
protected:

# define __ROPE_DEFINE_ALLOC(_Tp, __name) \
        typedef typename \
          _Alloc_traits<_Tp,_Allocator>::_Alloc_type __name##Alloc; \
        typedef typename \
          _Alloc_traits<_Tp,_Allocator>::allocator_type __name##Allocator; \
        static _Tp* __name##_allocate(size_t __n) \
                { return __name##Alloc::allocate(__n); } \
        void __name##_deallocate(_Tp *__p, size_t __n) \
                { __name##Alloc::deallocate(__p, __n); }
  __ROPE_DEFINE_ALLOCS(_Allocator);
# undef __ROPE_DEFINE_ALLOC
};

template <class _CharT, class _Alloc>
struct _Rope_rep_base
  : public _Rope_rep_alloc_base<_CharT,_Alloc,
                                _Alloc_traits<_CharT,_Alloc>::_S_instanceless>
{
  typedef _Rope_rep_alloc_base<_CharT,_Alloc,
                               _Alloc_traits<_CharT,_Alloc>::_S_instanceless>
          _Base;
  typedef typename _Base::allocator_type allocator_type;
  _Rope_rep_base(size_t __size, const allocator_type& __a)
    : _Base(__size, __a) {}
};    


template<class _CharT, class _Alloc>
struct _Rope_RopeRep : public _Rope_rep_base<_CharT,_Alloc>
# ifndef __GC
    , _Refcount_Base
# endif
{
    public:
    enum { _S_max_rope_depth = 45 };
    enum _Tag {_S_leaf, _S_concat, _S_substringfn, _S_function};
    _Tag _M_tag:8;
    bool _M_is_balanced:8;
    unsigned char _M_depth;
    __GC_CONST _CharT* _M_c_string;
                        /* Flattened version of string, if needed.  */
                        /* typically 0.                             */
                        /* If it's not 0, then the memory is owned  */
                        /* by this node.                            */
                        /* In the case of a leaf, this may point to */
                        /* the same memory as the data field.       */
    typedef typename _Rope_rep_base<_CharT,_Alloc>::allocator_type
                        allocator_type;
    _Rope_RopeRep(_Tag __t, int __d, bool __b, size_t __size,
                  allocator_type __a)
        : _Rope_rep_base<_CharT,_Alloc>(__size, __a),
#         ifndef __GC
          _Refcount_Base(1),
#         endif
          _M_tag(__t), _M_is_balanced(__b), _M_depth(__d), _M_c_string(0)
    { }
#   ifdef __GC
        void _M_incr () {}
#   endif
        static void _S_free_string(__GC_CONST _CharT*, size_t __len,
                                   allocator_type __a);
#       define __STL_FREE_STRING(__s, __l, __a) _S_free_string(__s, __l, __a);
                        // Deallocate data section of a leaf.
                        // This shouldn't be a member function.
                        // But its hard to do anything else at the
                        // moment, because it's templatized w.r.t.
                        // an allocator.
                        // Does nothing if __GC is defined.
#   ifndef __GC
          void _M_free_c_string();
          void _M_free_tree();
                        // Deallocate t. Assumes t is not 0.
          void _M_unref_nonnil()
          {
              if (0 == _M_decr()) _M_free_tree();
          }
          void _M_ref_nonnil()
          {
              _M_incr();
          }
          static void _S_unref(_Rope_RopeRep* __t)
          {
              if (0 != __t) {
                  __t->_M_unref_nonnil();
              }
          }
          static void _S_ref(_Rope_RopeRep* __t)
          {
              if (0 != __t) __t->_M_incr();
          }
          static void _S_free_if_unref(_Rope_RopeRep* __t)
          {
              if (0 != __t && 0 == __t->_M_ref_count) __t->_M_free_tree();
          }
#   else /* __GC */
          void _M_unref_nonnil() {}
          void _M_ref_nonnil() {}
          static void _S_unref(_Rope_RopeRep*) {}
          static void _S_ref(_Rope_RopeRep*) {}
          static void _S_free_if_unref(_Rope_RopeRep*) {}
#   endif

};

template<class _CharT, class _Alloc>
struct _Rope_RopeLeaf : public _Rope_RopeRep<_CharT,_Alloc> {
  public:
    // Apparently needed by VC++
    // The data fields of leaves are allocated with some
    // extra space, to accomodate future growth and for basic
    // character types, to hold a trailing eos character.
    enum { _S_alloc_granularity = 8 };
    static size_t _S_rounded_up_size(size_t __n) {
        size_t __size_with_eos;
             
        if (_S_is_basic_char_type((_CharT*)0)) {
            __size_with_eos = __n + 1;
        } else {
            __size_with_eos = __n;
        }
#       ifdef __GC
           return __size_with_eos;
#       else
           // Allow slop for in-place expansion.
           return (__size_with_eos + _S_alloc_granularity-1)
                        &~ (_S_alloc_granularity-1);
#       endif
    }
    __GC_CONST _CharT* _M_data; /* Not necessarily 0 terminated. */
                                /* The allocated size is         */
                                /* _S_rounded_up_size(size), except */
                                /* in the GC case, in which it   */
                                /* doesn't matter.               */
    typedef typename _Rope_rep_base<_CharT,_Alloc>::allocator_type
                        allocator_type;
    _Rope_RopeLeaf(__GC_CONST _CharT* __d, size_t __size, allocator_type __a)
        : _Rope_RopeRep<_CharT,_Alloc>(_S_leaf, 0, true, __size, __a),
          _M_data(__d)
        {
        __stl_assert(__size > 0);
        if (_S_is_basic_char_type((_CharT *)0)) {
            // already eos terminated.
            _M_c_string = __d;
        }
    }
        // The constructor assumes that d has been allocated with
        // the proper allocator and the properly padded size.
        // In contrast, the destructor deallocates the data:
# ifndef __GC
    ~_Rope_RopeLeaf() {
        if (_M_data != _M_c_string) {
            _M_free_c_string();
        }
        __STL_FREE_STRING(_M_data, _M_size, get_allocator());
    }
# endif
};

template<class _CharT, class _Alloc>
struct _Rope_RopeConcatenation : public _Rope_RopeRep<_CharT,_Alloc> {
  public:
    _Rope_RopeRep<_CharT,_Alloc>* _M_left;
    _Rope_RopeRep<_CharT,_Alloc>* _M_right;
    typedef typename _Rope_rep_base<_CharT,_Alloc>::allocator_type
                        allocator_type;
    _Rope_RopeConcatenation(_Rope_RopeRep<_CharT,_Alloc>* __l,
                             _Rope_RopeRep<_CharT,_Alloc>* __r,
                             allocator_type __a)

      : _Rope_RopeRep<_CharT,_Alloc>(_S_concat,
                                     max(__l->_M_depth, __r->_M_depth) + 1,
                                     false,
                                     __l->_M_size + __r->_M_size, __a),
        _M_left(__l), _M_right(__r)
      {}
# ifndef __GC
    ~_Rope_RopeConcatenation() {
        _M_free_c_string();
        _M_left->_M_unref_nonnil();
        _M_right->_M_unref_nonnil();
    }
# endif
};

template<class _CharT, class _Alloc>
struct _Rope_RopeFunction : public _Rope_RopeRep<_CharT,_Alloc> {
  public:
    char_producer<_CharT>* _M_fn;
#   ifndef __GC
      bool _M_delete_when_done; // Char_producer is owned by the
                                // rope and should be explicitly
                                // deleted when the rope becomes
                                // inaccessible.
#   else
      // In the GC case, we either register the rope for
      // finalization, or not.  Thus the field is unnecessary;
      // the information is stored in the collector data structures.
      // We do need a finalization procedure to be invoked by the
      // collector.
      static void _S_fn_finalization_proc(void * __tree, void *) {
        delete ((_Rope_RopeFunction *)__tree) -> _M_fn;
      }
#   endif
    typedef typename _Rope_rep_base<_CharT,_Alloc>::allocator_type
                                        allocator_type;
    _Rope_RopeFunction(char_producer<_CharT>* __f, size_t __size,
                        bool __d, allocator_type __a)
      : _Rope_RopeRep<_CharT,_Alloc>(_S_function, 0, true, __size, __a)
      , _M_fn(__f)
#       ifndef __GC
      , _M_delete_when_done(__d)
#       endif
    {
        __stl_assert(__size > 0);
#       ifdef __GC
            if (__d) {
                GC_REGISTER_FINALIZER(
                  this, _Rope_RopeFunction::_S_fn_finalization_proc, 0, 0, 0);
            }
#       endif
    }
# ifndef __GC
    ~_Rope_RopeFunction() {
          _M_free_c_string();
          if (_M_delete_when_done) {
              delete _M_fn;
          }
    }
# endif
};
// Substring results are usually represented using just
// concatenation nodes.  But in the case of very long flat ropes
// or ropes with a functional representation that isn't practical.
// In that case, we represent the __result as a special case of
// RopeFunction, whose char_producer points back to the rope itself.
// In all cases except repeated substring operations and
// deallocation, we treat the __result as a RopeFunction.
template<class _CharT, class _Alloc>
struct _Rope_RopeSubstring : public _Rope_RopeFunction<_CharT,_Alloc>,
                             public char_producer<_CharT> {
  public:
    // XXX this whole class should be rewritten.
    _Rope_RopeRep<_CharT,_Alloc>* _M_base;      // not 0
    size_t _M_start;
    virtual void operator()(size_t __start_pos, size_t __req_len,
                            _CharT* __buffer) {
        switch(_M_base->_M_tag) {
            case _S_function:
            case _S_substringfn:
              {
                char_producer<_CharT>* __fn =
                        ((_Rope_RopeFunction<_CharT,_Alloc>*)_M_base)->_M_fn;
                __stl_assert(__start_pos + __req_len <= _M_size);
                __stl_assert(_M_start + _M_size <= _M_base->_M_size);
                (*__fn)(__start_pos + _M_start, __req_len, __buffer);
              }
              break;
            case _S_leaf:
              {
                __GC_CONST _CharT* __s =
                        ((_Rope_RopeLeaf<_CharT,_Alloc>*)_M_base)->_M_data;
                uninitialized_copy_n(__s + __start_pos + _M_start, __req_len,
                                     __buffer);
              }
              break;
            default:
              __stl_assert(false);
        }
    }
    typedef typename _Rope_rep_base<_CharT,_Alloc>::allocator_type
        allocator_type;
    _Rope_RopeSubstring(_Rope_RopeRep<_CharT,_Alloc>* __b, size_t __s,
                          size_t __l, allocator_type __a)
      : _Rope_RopeFunction<_CharT,_Alloc>(this, __l, false, __a),
        char_producer<_CharT>(),
        _M_base(__b),
        _M_start(__s)
    {
        __stl_assert(__l > 0);
        __stl_assert(__s + __l <= __b->_M_size);
#       ifndef __GC
            _M_base->_M_ref_nonnil();
#       endif
        _M_tag = _S_substringfn;
    }
    virtual ~_Rope_RopeSubstring()
      { 
#       ifndef __GC
          _M_base->_M_unref_nonnil();
          // _M_free_c_string();  -- done by parent class
#       endif
      }
};


// Self-destructing pointers to Rope_rep.
// These are not conventional smart pointers.  Their
// only purpose in life is to ensure that unref is called
// on the pointer either at normal exit or if an exception
// is raised.  It is the caller's responsibility to
// adjust reference counts when these pointers are initialized
// or assigned to.  (This convention significantly reduces
// the number of potentially expensive reference count
// updates.)
#ifndef __GC
  template<class _CharT, class _Alloc>
  struct _Rope_self_destruct_ptr {
    _Rope_RopeRep<_CharT,_Alloc>* _M_ptr;
    ~_Rope_self_destruct_ptr() 
      { _Rope_RopeRep<_CharT,_Alloc>::_S_unref(_M_ptr); }
#   ifdef __STL_USE_EXCEPTIONS
        _Rope_self_destruct_ptr() : _M_ptr(0) {};
#   else
        _Rope_self_destruct_ptr() {};
#   endif
    _Rope_self_destruct_ptr(_Rope_RopeRep<_CharT,_Alloc>* __p) : _M_ptr(__p) {}
    _Rope_RopeRep<_CharT,_Alloc>& operator*() { return *_M_ptr; }
    _Rope_RopeRep<_CharT,_Alloc>* operator->() { return _M_ptr; }
    operator _Rope_RopeRep<_CharT,_Alloc>*() { return _M_ptr; }
    _Rope_self_destruct_ptr& operator= (_Rope_RopeRep<_CharT,_Alloc>* __x)
        { _M_ptr = __x; return *this; }
  };
#endif

// Dereferencing a nonconst iterator has to return something
// that behaves almost like a reference.  It's not possible to
// return an actual reference since assignment requires extra
// work.  And we would get into the same problems as with the
// CD2 version of basic_string.
template<class _CharT, class _Alloc>
class _Rope_char_ref_proxy {
    friend class rope<_CharT,_Alloc>;
    friend class _Rope_iterator<_CharT,_Alloc>;
    friend class _Rope_char_ptr_proxy<_CharT,_Alloc>;
#   ifdef __GC
        typedef _Rope_RopeRep<_CharT,_Alloc>* _Self_destruct_ptr;
#   else
        typedef _Rope_self_destruct_ptr<_CharT,_Alloc> _Self_destruct_ptr;
#   endif
    typedef _Rope_RopeRep<_CharT,_Alloc> _RopeRep;
    typedef rope<_CharT,_Alloc> _My_rope;
    size_t _M_pos;
    _CharT _M_current;
    bool _M_current_valid;
    _My_rope* _M_root;     // The whole rope.
  public:
    _Rope_char_ref_proxy(_My_rope* __r, size_t __p)
      :  _M_pos(__p), _M_current_valid(false), _M_root(__r) {}
    _Rope_char_ref_proxy(const _Rope_char_ref_proxy& __x)
      : _M_pos(__x._M_pos), _M_current_valid(false), _M_root(__x._M_root) {}
        // Don't preserve cache if the reference can outlive the
        // expression.  We claim that's not possible without calling
        // a copy constructor or generating reference to a proxy
        // reference.  We declare the latter to have undefined semantics.
    _Rope_char_ref_proxy(_My_rope* __r, size_t __p, _CharT __c)
      : _M_pos(__p), _M_current(__c), _M_current_valid(true), _M_root(__r) {}
    inline operator _CharT () const;
    _Rope_char_ref_proxy& operator= (_CharT __c);
    _Rope_char_ptr_proxy<_CharT,_Alloc> operator& () const;
    _Rope_char_ref_proxy& operator= (const _Rope_char_ref_proxy& __c) {
        return operator=((_CharT)__c); 
    }
};

template<class _CharT, class __Alloc>
inline void swap(_Rope_char_ref_proxy <_CharT, __Alloc > __a,
                 _Rope_char_ref_proxy <_CharT, __Alloc > __b) {
    _CharT __tmp = __a;
    __a = __b;
    __b = __tmp;
}

template<class _CharT, class _Alloc>
class _Rope_char_ptr_proxy {
    // XXX this class should be rewritten.
    friend class _Rope_char_ref_proxy<_CharT,_Alloc>;
    size_t _M_pos;
    rope<_CharT,_Alloc>* _M_root;     // The whole rope.
  public:
    _Rope_char_ptr_proxy(const _Rope_char_ref_proxy<_CharT,_Alloc>& __x) 
      : _M_pos(__x._M_pos), _M_root(__x._M_root) {}
    _Rope_char_ptr_proxy(const _Rope_char_ptr_proxy& __x)
      : _M_pos(__x._M_pos), _M_root(__x._M_root) {}
    _Rope_char_ptr_proxy() {}
    _Rope_char_ptr_proxy(_CharT* __x) : _M_root(0), _M_pos(0) {
        __stl_assert(0 == __x);
    }
    _Rope_char_ptr_proxy& 
    operator= (const _Rope_char_ptr_proxy& __x) {
        _M_pos = __x._M_pos;
        _M_root = __x._M_root;
        return *this;
    }
    template<class _CharT2, class _Alloc2>
    friend bool operator== (const _Rope_char_ptr_proxy<_CharT2,_Alloc2>& __x,
                            const _Rope_char_ptr_proxy<_CharT2,_Alloc2>& __y);
    _Rope_char_ref_proxy<_CharT,_Alloc> operator*() const {
        return _Rope_char_ref_proxy<_CharT,_Alloc>(_M_root, _M_pos);
    }
};


// Rope iterators:
// Unlike in the C version, we cache only part of the stack
// for rope iterators, since they must be efficiently copyable.
// When we run out of cache, we have to reconstruct the iterator
// value.
// Pointers from iterators are not included in reference counts.
// Iterators are assumed to be thread private.  Ropes can
// be shared.

template<class _CharT, class _Alloc>
class _Rope_iterator_base
  : public random_access_iterator<_CharT, ptrdiff_t> {
    friend class rope<_CharT,_Alloc>;
  public:
    typedef _Alloc _allocator_type; // used in _Rope_rotate, VC++ workaround
    typedef _Rope_RopeRep<_CharT,_Alloc> _RopeRep;
        // Borland doesnt want this to be protected.
  protected:
    enum { _S_path_cache_len = 4 }; // Must be <= 9.
    enum { _S_iterator_buf_len = 15 };
    size_t _M_current_pos;
    _RopeRep* _M_root;     // The whole rope.
    size_t _M_leaf_pos;    // Starting position for current leaf
    __GC_CONST _CharT* _M_buf_start;
                        // Buffer possibly
                        // containing current char.
    __GC_CONST _CharT* _M_buf_ptr;
                        // Pointer to current char in buffer.
                        // != 0 ==> buffer valid.
    __GC_CONST _CharT* _M_buf_end;
                        // One past __last valid char in buffer.
    // What follows is the path cache.  We go out of our
    // way to make this compact.
    // Path_end contains the bottom section of the path from
    // the root to the current leaf.
    const _RopeRep* _M_path_end[_S_path_cache_len];
    int _M_leaf_index;     // Last valid __pos in path_end;
                        // _M_path_end[0] ... _M_path_end[leaf_index-1]
                        // point to concatenation nodes.
    unsigned char _M_path_directions;
                          // (path_directions >> __i) & 1 is 1
                          // iff we got from _M_path_end[leaf_index - __i - 1]
                          // to _M_path_end[leaf_index - __i] by going to the
                          // __right. Assumes path_cache_len <= 9.
    _CharT _M_tmp_buf[_S_iterator_buf_len];
                        // Short buffer for surrounding chars.
                        // This is useful primarily for 
                        // RopeFunctions.  We put the buffer
                        // here to avoid locking in the
                        // multithreaded case.
    // The cached path is generally assumed to be valid
    // only if the buffer is valid.
    static void _S_setbuf(_Rope_iterator_base& __x);
                                        // Set buffer contents given
                                        // path cache.
    static void _S_setcache(_Rope_iterator_base& __x);
                                        // Set buffer contents and
                                        // path cache.
    static void _S_setcache_for_incr(_Rope_iterator_base& __x);
                                        // As above, but assumes path
                                        // cache is valid for previous posn.
    _Rope_iterator_base() {}
    _Rope_iterator_base(_RopeRep* __root, size_t __pos)
      : _M_current_pos(__pos), _M_root(__root), _M_buf_ptr(0) {}
    void _M_incr(size_t __n);
    void _M_decr(size_t __n);
  public:
    size_t index() const { return _M_current_pos; }
    _Rope_iterator_base(const _Rope_iterator_base& __x) {
        if (0 != __x._M_buf_ptr) {
            *this = __x;
        } else {
            _M_current_pos = __x._M_current_pos;
            _M_root = __x._M_root;
            _M_buf_ptr = 0;
        }
    }
};

template<class _CharT, class _Alloc> class _Rope_iterator;

template<class _CharT, class _Alloc>
class _Rope_const_iterator : public _Rope_iterator_base<_CharT,_Alloc> {
    friend class rope<_CharT,_Alloc>;
  protected:
      typedef _Rope_RopeRep<_CharT,_Alloc> _RopeRep;
      // The one from the base class may not be directly visible.
    _Rope_const_iterator(const _RopeRep* __root, size_t __pos):
                   _Rope_iterator_base<_CharT,_Alloc>(
                     const_cast<_RopeRep*>(__root), __pos)
                   // Only nonconst iterators modify root ref count
    {}
  public:
    typedef _CharT reference;   // Really a value.  Returning a reference
                                // Would be a mess, since it would have
                                // to be included in refcount.
    typedef const _CharT* pointer;

  public:
    _Rope_const_iterator() {};
    _Rope_const_iterator(const _Rope_const_iterator& __x) :
                                _Rope_iterator_base<_CharT,_Alloc>(__x) { }
    _Rope_const_iterator(const _Rope_iterator<_CharT,_Alloc>& __x);
    _Rope_const_iterator(const rope<_CharT,_Alloc>& __r, size_t __pos) :
        _Rope_iterator_base<_CharT,_Alloc>(__r._M_tree_ptr, __pos) {}
    _Rope_const_iterator& operator= (const _Rope_const_iterator& __x) {
        if (0 != __x._M_buf_ptr) {
            *(static_cast<_Rope_iterator_base<_CharT,_Alloc>*>(this)) = __x;
        } else {
            _M_current_pos = __x._M_current_pos;
            _M_root = __x._M_root;
            _M_buf_ptr = 0;
        }
        return(*this);
    }
    reference operator*() {
        if (0 == _M_buf_ptr) _S_setcache(*this);
        return *_M_buf_ptr;
    }
    _Rope_const_iterator& operator++() {
        __GC_CONST _CharT* __next;
        if (0 != _M_buf_ptr && (__next = _M_buf_ptr + 1) < _M_buf_end) {
            _M_buf_ptr = __next;
            ++_M_current_pos;
        } else {
            _M_incr(1);
        }
        return *this;
    }
    _Rope_const_iterator& operator+=(ptrdiff_t __n) {
        if (__n >= 0) {
            _M_incr(__n);
        } else {
            _M_decr(-__n);
        }
        return *this;
    }
    _Rope_const_iterator& operator--() {
        _M_decr(1);
        return *this;
    }
    _Rope_const_iterator& operator-=(ptrdiff_t __n) {
        if (__n >= 0) {
            _M_decr(__n);
        } else {
            _M_incr(-__n);
        }
        return *this;
    }
    _Rope_const_iterator operator++(int) {
        size_t __old_pos = _M_current_pos;
        _M_incr(1);
        return _Rope_const_iterator<_CharT,_Alloc>(_M_root, __old_pos);
        // This makes a subsequent dereference expensive.
        // Perhaps we should instead copy the iterator
        // if it has a valid cache?
    }
    _Rope_const_iterator operator--(int) {
        size_t __old_pos = _M_current_pos;
        _M_decr(1);
        return _Rope_const_iterator<_CharT,_Alloc>(_M_root, __old_pos);
    }
    template<class _CharT2, class _Alloc2>
    friend _Rope_const_iterator<_CharT2,_Alloc2> operator-
        (const _Rope_const_iterator<_CharT2,_Alloc2>& __x,
         ptrdiff_t __n);
    template<class _CharT2, class _Alloc2>
    friend _Rope_const_iterator<_CharT2,_Alloc2> operator+
        (const _Rope_const_iterator<_CharT2,_Alloc2>& __x,
         ptrdiff_t __n);
    template<class _CharT2, class _Alloc2>
    friend _Rope_const_iterator<_CharT2,_Alloc2> operator+
        (ptrdiff_t __n,
         const _Rope_const_iterator<_CharT2,_Alloc2>& __x);
    reference operator[](size_t __n) {
        return rope<_CharT,_Alloc>::_S_fetch(_M_root, _M_current_pos + __n);
    }

    template<class _CharT2, class _Alloc2>
    friend bool operator==
        (const _Rope_const_iterator<_CharT2,_Alloc2>& __x,
         const _Rope_const_iterator<_CharT2,_Alloc2>& __y);
    template<class _CharT2, class _Alloc2>
    friend bool operator< 
        (const _Rope_const_iterator<_CharT2,_Alloc2>& __x,
         const _Rope_const_iterator<_CharT2,_Alloc2>& __y);
    template<class _CharT2, class _Alloc2>
    friend ptrdiff_t operator-
        (const _Rope_const_iterator<_CharT2,_Alloc2>& __x,
         const _Rope_const_iterator<_CharT2,_Alloc2>& __y);
};

template<class _CharT, class _Alloc>
class _Rope_iterator : public _Rope_iterator_base<_CharT,_Alloc> {
    friend class rope<_CharT,_Alloc>;
  protected:
    rope<_CharT,_Alloc>* _M_root_rope;
        // root is treated as a cached version of this,
        // and is used to detect changes to the underlying
        // rope.
        // Root is included in the reference count.
        // This is necessary so that we can detect changes reliably.
        // Unfortunately, it requires careful bookkeeping for the
        // nonGC case.
    _Rope_iterator(rope<_CharT,_Alloc>* __r, size_t __pos)
      : _Rope_iterator_base<_CharT,_Alloc>(__r->_M_tree_ptr, __pos),
        _M_root_rope(__r) 
       { _RopeRep::_S_ref(_M_root); if (!(__r -> empty()))_S_setcache(*this); }

    void _M_check();
  public:
    typedef _Rope_char_ref_proxy<_CharT,_Alloc>  reference;
    typedef _Rope_char_ref_proxy<_CharT,_Alloc>* pointer;

  public:
    rope<_CharT,_Alloc>& container() { return *_M_root_rope; }
    _Rope_iterator() {
        _M_root = 0;  // Needed for reference counting.
    };
    _Rope_iterator(const _Rope_iterator& __x) :
        _Rope_iterator_base<_CharT,_Alloc>(__x) {
        _M_root_rope = __x._M_root_rope;
        _RopeRep::_S_ref(_M_root);
    }
    _Rope_iterator(rope<_CharT,_Alloc>& __r, size_t __pos);
    ~_Rope_iterator() {
        _RopeRep::_S_unref(_M_root);
    }
    _Rope_iterator& operator= (const _Rope_iterator& __x) {
        _RopeRep* __old = _M_root;

        _RopeRep::_S_ref(__x._M_root);
        if (0 != __x._M_buf_ptr) {
            _M_root_rope = __x._M_root_rope;
            *(static_cast<_Rope_iterator_base<_CharT,_Alloc>*>(this)) = __x;
        } else {
            _M_current_pos = __x._M_current_pos;
            _M_root = __x._M_root;
            _M_root_rope = __x._M_root_rope;
            _M_buf_ptr = 0;
        }
        _RopeRep::_S_unref(__old);
        return(*this);
    }
    reference operator*() {
        _M_check();
        if (0 == _M_buf_ptr) {
            return _Rope_char_ref_proxy<_CharT,_Alloc>(
               _M_root_rope, _M_current_pos);
        } else {
            return _Rope_char_ref_proxy<_CharT,_Alloc>(
               _M_root_rope, _M_current_pos, *_M_buf_ptr);
        }
    }
    _Rope_iterator& operator++() {
        _M_incr(1);
        return *this;
    }
    _Rope_iterator& operator+=(ptrdiff_t __n) {
        if (__n >= 0) {
            _M_incr(__n);
        } else {
            _M_decr(-__n);
        }
        return *this;
    }
    _Rope_iterator& operator--() {
        _M_decr(1);
        return *this;
    }
    _Rope_iterator& operator-=(ptrdiff_t __n) {
        if (__n >= 0) {
            _M_decr(__n);
        } else {
            _M_incr(-__n);
        }
        return *this;
    }
    _Rope_iterator operator++(int) {
        size_t __old_pos = _M_current_pos;
        _M_incr(1);
        return _Rope_iterator<_CharT,_Alloc>(_M_root_rope, __old_pos);
    }
    _Rope_iterator operator--(int) {
        size_t __old_pos = _M_current_pos;
        _M_decr(1);
        return _Rope_iterator<_CharT,_Alloc>(_M_root_rope, __old_pos);
    }
    reference operator[](ptrdiff_t __n) {
        return _Rope_char_ref_proxy<_CharT,_Alloc>(
          _M_root_rope, _M_current_pos + __n);
    }

    template<class _CharT2, class _Alloc2>
    friend bool operator==
        (const _Rope_iterator<_CharT2,_Alloc2>& __x,
         const _Rope_iterator<_CharT2,_Alloc2>& __y);
    template<class _CharT2, class _Alloc2>
    friend bool operator<
        (const _Rope_iterator<_CharT2,_Alloc2>& __x,
         const _Rope_iterator<_CharT2,_Alloc2>& __y);
    template<class _CharT2, class _Alloc2>
    friend ptrdiff_t operator-
        (const _Rope_iterator<_CharT2,_Alloc2>& __x,
         const _Rope_iterator<_CharT2,_Alloc2>& __y);
    template<class _CharT2, class _Alloc2>
    friend _Rope_iterator<_CharT2,_Alloc2> operator-
        (const _Rope_iterator<_CharT2,_Alloc2>& __x,
         ptrdiff_t __n);
    template<class _CharT2, class _Alloc2>
    friend _Rope_iterator<_CharT2,_Alloc2> operator+
        (const _Rope_iterator<_CharT2,_Alloc2>& __x,
         ptrdiff_t __n);
    template<class _CharT2, class _Alloc2>
    friend _Rope_iterator<_CharT2,_Alloc2> operator+
        (ptrdiff_t __n,
         const _Rope_iterator<_CharT2,_Alloc2>& __x);
};

//  The rope base class encapsulates
//  the differences between SGI-style allocators and standard-conforming
//  allocators.

// Base class for ordinary allocators.
template <class _CharT, class _Allocator, bool _IsStatic>
class _Rope_alloc_base {
public:
  typedef _Rope_RopeRep<_CharT,_Allocator> _RopeRep;
  typedef typename _Alloc_traits<_CharT,_Allocator>::allocator_type
          allocator_type;
  allocator_type get_allocator() const { return _M_data_allocator; }
  _Rope_alloc_base(_RopeRep *__t, const allocator_type& __a)
        : _M_tree_ptr(__t), _M_data_allocator(__a) {}
  _Rope_alloc_base(const allocator_type& __a)
        : _M_data_allocator(__a) {}
  
protected:
  // The only data members of a rope:
    allocator_type _M_data_allocator;
    _RopeRep* _M_tree_ptr;

# define __ROPE_DEFINE_ALLOC(_Tp, __name) \
        typedef typename \
          _Alloc_traits<_Tp,_Allocator>::allocator_type __name##Allocator; \
        _Tp* __name##_allocate(size_t __n) const \
          { return __name##Allocator(_M_data_allocator).allocate(__n); } \
        void __name##_deallocate(_Tp *__p, size_t __n) const \
                { __name##Allocator(_M_data_allocator).deallocate(__p, __n); }
  __ROPE_DEFINE_ALLOCS(_Allocator)
# undef __ROPE_DEFINE_ALLOC
};

// Specialization for allocators that have the property that we don't
//  actually have to store an allocator object.  
template <class _CharT, class _Allocator>
class _Rope_alloc_base<_CharT,_Allocator,true> {
public:
  typedef _Rope_RopeRep<_CharT,_Allocator> _RopeRep;
  typedef typename _Alloc_traits<_CharT,_Allocator>::allocator_type
          allocator_type;
  allocator_type get_allocator() const { return allocator_type(); }
  _Rope_alloc_base(_RopeRep *__t, const allocator_type&)
                : _M_tree_ptr(__t) {}
  _Rope_alloc_base(const allocator_type&) {}
  
protected:
  // The only data member of a rope:
    _RopeRep *_M_tree_ptr;

# define __ROPE_DEFINE_ALLOC(_Tp, __name) \
        typedef typename \
          _Alloc_traits<_Tp,_Allocator>::_Alloc_type __name##Alloc; \
        typedef typename \
          _Alloc_traits<_Tp,_Allocator>::allocator_type __name##Allocator; \
        static _Tp* __name##_allocate(size_t __n) \
          { return __name##Alloc::allocate(__n); } \
        static void __name##_deallocate(_Tp *__p, size_t __n) \
          { __name##Alloc::deallocate(__p, __n); }
  __ROPE_DEFINE_ALLOCS(_Allocator)
# undef __ROPE_DEFINE_ALLOC
};

template <class _CharT, class _Alloc>
struct _Rope_base 
  : public _Rope_alloc_base<_CharT,_Alloc,
                            _Alloc_traits<_CharT,_Alloc>::_S_instanceless>
{
  typedef _Rope_alloc_base<_CharT,_Alloc,
                            _Alloc_traits<_CharT,_Alloc>::_S_instanceless>
          _Base;
  typedef typename _Base::allocator_type allocator_type;
  typedef _Rope_RopeRep<_CharT,_Alloc> _RopeRep;
        // The one in _Base may not be visible due to template rules.
  _Rope_base(_RopeRep* __t, const allocator_type& __a) : _Base(__t, __a) {}
  _Rope_base(const allocator_type& __a) : _Base(__a) {}
};    


template <class _CharT, class _Alloc>
class rope : public _Rope_base<_CharT,_Alloc> {
    public:
        typedef _CharT value_type;
        typedef ptrdiff_t difference_type;
        typedef size_t size_type;
        typedef _CharT const_reference;
        typedef const _CharT* const_pointer;
        typedef _Rope_iterator<_CharT,_Alloc> iterator;
        typedef _Rope_const_iterator<_CharT,_Alloc> const_iterator;
        typedef _Rope_char_ref_proxy<_CharT,_Alloc> reference;
        typedef _Rope_char_ptr_proxy<_CharT,_Alloc> pointer;

        friend class _Rope_iterator<_CharT,_Alloc>;
        friend class _Rope_const_iterator<_CharT,_Alloc>;
        friend struct _Rope_RopeRep<_CharT,_Alloc>;
        friend class _Rope_iterator_base<_CharT,_Alloc>;
        friend class _Rope_char_ptr_proxy<_CharT,_Alloc>;
        friend class _Rope_char_ref_proxy<_CharT,_Alloc>;
        friend struct _Rope_RopeSubstring<_CharT,_Alloc>;

    protected:
        typedef _Rope_base<_CharT,_Alloc> _Base;
        typedef typename _Base::allocator_type allocator_type;
        using _Base::_M_tree_ptr;
        typedef __GC_CONST _CharT* _Cstrptr;

        static _CharT _S_empty_c_str[1];

        static bool _S_is0(_CharT __c) { return __c == _S_eos((_CharT*)0); }
        enum { _S_copy_max = 23 };
                // For strings shorter than _S_copy_max, we copy to
                // concatenate.

        typedef _Rope_RopeRep<_CharT,_Alloc> _RopeRep;
        typedef _Rope_RopeConcatenation<_CharT,_Alloc> _RopeConcatenation;
        typedef _Rope_RopeLeaf<_CharT,_Alloc> _RopeLeaf;
        typedef _Rope_RopeFunction<_CharT,_Alloc> _RopeFunction;
        typedef _Rope_RopeSubstring<_CharT,_Alloc> _RopeSubstring;

        // Retrieve a character at the indicated position.
        static _CharT _S_fetch(_RopeRep* __r, size_type __pos);

#       ifndef __GC
            // Obtain a pointer to the character at the indicated position.
            // The pointer can be used to change the character.
            // If such a pointer cannot be produced, as is frequently the
            // case, 0 is returned instead.
            // (Returns nonzero only if all nodes in the path have a refcount
            // of 1.)
            static _CharT* _S_fetch_ptr(_RopeRep* __r, size_type __pos);
#       endif

        static bool _S_apply_to_pieces(
                                // should be template parameter
                                _Rope_char_consumer<_CharT>& __c,
                                const _RopeRep* __r,
                                size_t __begin, size_t __end);
                                // begin and end are assumed to be in range.

#       ifndef __GC
          static void _S_unref(_RopeRep* __t)
          {
              _RopeRep::_S_unref(__t);
          }
          static void _S_ref(_RopeRep* __t)
          {
              _RopeRep::_S_ref(__t);
          }
#       else /* __GC */
          static void _S_unref(_RopeRep*) {}
          static void _S_ref(_RopeRep*) {}
#       endif


#       ifdef __GC
            typedef _Rope_RopeRep<_CharT,_Alloc>* _Self_destruct_ptr;
#       else
            typedef _Rope_self_destruct_ptr<_CharT,_Alloc> _Self_destruct_ptr;
#       endif

        // _Result is counted in refcount.
        static _RopeRep* _S_substring(_RopeRep* __base,
                                    size_t __start, size_t __endp1);

        static _RopeRep* _S_concat_char_iter(_RopeRep* __r,
                                          const _CharT* __iter, size_t __slen);
                // Concatenate rope and char ptr, copying __s.
                // Should really take an arbitrary iterator.
                // Result is counted in refcount.
        static _RopeRep* _S_destr_concat_char_iter(_RopeRep* __r,
                                          const _CharT* __iter, size_t __slen)
                // As above, but one reference to __r is about to be
                // destroyed.  Thus the pieces may be recycled if all
                // relevent reference counts are 1.
#           ifdef __GC
                // We can't really do anything since refcounts are unavailable.
                { return _S_concat_char_iter(__r, __iter, __slen); }
#           else
                ;
#           endif

        static _RopeRep* _S_concat(_RopeRep* __left, _RopeRep* __right);
                // General concatenation on _RopeRep.  _Result
                // has refcount of 1.  Adjusts argument refcounts.

   public:
        void apply_to_pieces( size_t __begin, size_t __end,
                              _Rope_char_consumer<_CharT>& __c) const {
            _S_apply_to_pieces(__c, _M_tree_ptr, __begin, __end);
        }


   protected:

        static size_t _S_rounded_up_size(size_t __n) {
            return _RopeLeaf::_S_rounded_up_size(__n);
        }

        static size_t _S_allocated_capacity(size_t __n) {
            if (_S_is_basic_char_type((_CharT*)0)) {
                return _S_rounded_up_size(__n) - 1;
            } else {
                return _S_rounded_up_size(__n);
            }
        }
                
        // Allocate and construct a RopeLeaf using the supplied allocator
        // Takes ownership of s instead of copying.
        static _RopeLeaf* _S_new_RopeLeaf(__GC_CONST _CharT *__s,
                                          size_t __size, allocator_type __a)
        {
            _RopeLeaf* __space = _LAllocator(__a).allocate(1);
            return new(__space) _RopeLeaf(__s, __size, __a);
        }

        static _RopeConcatenation* _S_new_RopeConcatenation(
                        _RopeRep* __left, _RopeRep* __right,
                        allocator_type __a)
        {
            _RopeConcatenation* __space = _CAllocator(__a).allocate(1);
            return new(__space) _RopeConcatenation(__left, __right, __a);
        }

        static _RopeFunction* _S_new_RopeFunction(char_producer<_CharT>* __f,
                size_t __size, bool __d, allocator_type __a)
        {
            _RopeFunction* __space = _FAllocator(__a).allocate(1);
            return new(__space) _RopeFunction(__f, __size, __d, __a);
        }

        static _RopeSubstring* _S_new_RopeSubstring(
                _Rope_RopeRep<_CharT,_Alloc>* __b, size_t __s,
                size_t __l, allocator_type __a)
        {
            _RopeSubstring* __space = _SAllocator(__a).allocate(1);
            return new(__space) _RopeSubstring(__b, __s, __l, __a);
        }

          static
          _RopeLeaf* _S_RopeLeaf_from_unowned_char_ptr(const _CharT *__s,
                       size_t __size, allocator_type __a)
#         define __STL_ROPE_FROM_UNOWNED_CHAR_PTR(__s, __size, __a) \
                _S_RopeLeaf_from_unowned_char_ptr(__s, __size, __a)     
        {
            if (0 == __size) return 0;
            _CharT* __buf = __a.allocate(_S_rounded_up_size(__size));

            uninitialized_copy_n(__s, __size, __buf);
            _S_cond_store_eos(__buf[__size]);
            __STL_TRY {
              return _S_new_RopeLeaf(__buf, __size, __a);
            }
            __STL_UNWIND(_RopeRep::__STL_FREE_STRING(__buf, __size, __a))
        }
            

        // Concatenation of nonempty strings.
        // Always builds a concatenation node.
        // Rebalances if the result is too deep.
        // Result has refcount 1.
        // Does not increment left and right ref counts even though
        // they are referenced.
        static _RopeRep*
        _S_tree_concat(_RopeRep* __left, _RopeRep* __right);

        // Concatenation helper functions
        static _RopeLeaf*
        _S_leaf_concat_char_iter(_RopeLeaf* __r,
                                 const _CharT* __iter, size_t __slen);
                // Concatenate by copying leaf.
                // should take an arbitrary iterator
                // result has refcount 1.
#       ifndef __GC
          static _RopeLeaf* _S_destr_leaf_concat_char_iter
                        (_RopeLeaf* __r, const _CharT* __iter, size_t __slen);
          // A version that potentially clobbers __r if __r->_M_ref_count == 1.
#       endif

        private:

        static size_t _S_char_ptr_len(const _CharT* __s);
                        // slightly generalized strlen

        rope(_RopeRep* __t, const allocator_type& __a = allocator_type())
          : _Base(__t,__a) { }


        // Copy __r to the _CharT buffer.
        // Returns __buffer + __r->_M_size.
        // Assumes that buffer is uninitialized.
        static _CharT* _S_flatten(_RopeRep* __r, _CharT* __buffer);

        // Again, with explicit starting position and length.
        // Assumes that buffer is uninitialized.
        static _CharT* _S_flatten(_RopeRep* __r,
                                  size_t __start, size_t __len,
                                  _CharT* __buffer);

        static const unsigned long 
          _S_min_len[_RopeRep::_S_max_rope_depth + 1];

        static bool _S_is_balanced(_RopeRep* __r)
                { return (__r->_M_size >= _S_min_len[__r->_M_depth]); }

        static bool _S_is_almost_balanced(_RopeRep* __r)
                { return (__r->_M_depth == 0 ||
                          __r->_M_size >= _S_min_len[__r->_M_depth - 1]); }

        static bool _S_is_roughly_balanced(_RopeRep* __r)
                { return (__r->_M_depth <= 1 ||
                          __r->_M_size >= _S_min_len[__r->_M_depth - 2]); }

        // Assumes the result is not empty.
        static _RopeRep* _S_concat_and_set_balanced(_RopeRep* __left,
                                                     _RopeRep* __right)
        {
            _RopeRep* __result = _S_concat(__left, __right);
            if (_S_is_balanced(__result)) __result->_M_is_balanced = true;
            return __result;
        }

        // The basic rebalancing operation.  Logically copies the
        // rope.  The result has refcount of 1.  The client will
        // usually decrement the reference count of __r.
        // The result is within height 2 of balanced by the above
        // definition.
        static _RopeRep* _S_balance(_RopeRep* __r);

        // Add all unbalanced subtrees to the forest of balanceed trees.
        // Used only by balance.
        static void _S_add_to_forest(_RopeRep*__r, _RopeRep** __forest);
        
        // Add __r to forest, assuming __r is already balanced.
        static void _S_add_leaf_to_forest(_RopeRep* __r, _RopeRep** __forest);

        // Print to stdout, exposing structure
        static void _S_dump(_RopeRep* __r, int __indent = 0);

        // Return -1, 0, or 1 if __x < __y, __x == __y, or __x > __y resp.
        static int _S_compare(const _RopeRep* __x, const _RopeRep* __y);

   public:
        bool empty() const { return 0 == _M_tree_ptr; }

        // Comparison member function.  This is public only for those
        // clients that need a ternary comparison.  Others
        // should use the comparison operators below.
        int compare(const rope& __y) const {
            return _S_compare(_M_tree_ptr, __y._M_tree_ptr);
        }

        rope(const _CharT* __s, const allocator_type& __a = allocator_type())
        : _Base(__STL_ROPE_FROM_UNOWNED_CHAR_PTR(__s, _S_char_ptr_len(__s),
                                                 __a),__a)
        { }

        rope(const _CharT* __s, size_t __len,
             const allocator_type& __a = allocator_type())
        : _Base(__STL_ROPE_FROM_UNOWNED_CHAR_PTR(__s, __len, __a), __a)
        { }

        // Should perhaps be templatized with respect to the iterator type
        // and use Sequence_buffer.  (It should perhaps use sequence_buffer
        // even now.)
        rope(const _CharT *__s, const _CharT *__e,
             const allocator_type& __a = allocator_type())
        : _Base(__STL_ROPE_FROM_UNOWNED_CHAR_PTR(__s, __e - __s, __a), __a)
        { }

        rope(const const_iterator& __s, const const_iterator& __e,
             const allocator_type& __a = allocator_type())
        : _Base(_S_substring(__s._M_root, __s._M_current_pos,
                             __e._M_current_pos), __a)
        { }

        rope(const iterator& __s, const iterator& __e,
             const allocator_type& __a = allocator_type())
        : _Base(_S_substring(__s._M_root, __s._M_current_pos,
                             __e._M_current_pos), __a)
        { }

        rope(_CharT __c, const allocator_type& __a = allocator_type())
        : _Base(__a)
        {
            _CharT* __buf = _Data_allocate(_S_rounded_up_size(1));

            construct(__buf, __c);
            __STL_TRY {
                _M_tree_ptr = _S_new_RopeLeaf(__buf, 1, __a);
            }
            __STL_UNWIND(_RopeRep::__STL_FREE_STRING(__buf, 1, __a))
        }

        rope(size_t __n, _CharT __c,
             const allocator_type& __a = allocator_type());

        rope(const allocator_type& __a = allocator_type())
        : _Base(0, __a) {}

        // Construct a rope from a function that can compute its members
        rope(char_producer<_CharT> *__fn, size_t __len, bool __delete_fn,
             const allocator_type& __a = allocator_type())
            : _Base(__a)
        {
            _M_tree_ptr = (0 == __len) ?
               0 : _S_new_RopeFunction(__fn, __len, __delete_fn, __a);
        }

        rope(const rope& __x, const allocator_type& __a = allocator_type())
        : _Base(__x._M_tree_ptr, __a)
        {
            _S_ref(_M_tree_ptr);
        }

        ~rope()
        {
            _S_unref(_M_tree_ptr);
        }

        rope& operator=(const rope& __x)
        {
            _RopeRep* __old = _M_tree_ptr;
            __stl_assert(get_allocator() == __x.get_allocator());
            _M_tree_ptr = __x._M_tree_ptr;
            _S_ref(_M_tree_ptr);
            _S_unref(__old);
            return(*this);
        }

        void clear()
        {
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = 0;
        }

        void push_back(_CharT __x)
        {
            _RopeRep* __old = _M_tree_ptr;
            _M_tree_ptr = _S_destr_concat_char_iter(_M_tree_ptr, &__x, 1);
            _S_unref(__old);
        }

        void pop_back()
        {
            _RopeRep* __old = _M_tree_ptr;
            _M_tree_ptr = 
              _S_substring(_M_tree_ptr, 0, _M_tree_ptr->_M_size - 1);
            _S_unref(__old);
        }

        _CharT back() const
        {
            return _S_fetch(_M_tree_ptr, _M_tree_ptr->_M_size - 1);
        }

        void push_front(_CharT __x)
        {
            _RopeRep* __old = _M_tree_ptr;
            _RopeRep* __left =
              __STL_ROPE_FROM_UNOWNED_CHAR_PTR(&__x, 1, get_allocator());
            __STL_TRY {
              _M_tree_ptr = _S_concat(__left, _M_tree_ptr);
              _S_unref(__old);
              _S_unref(__left);
            }
            __STL_UNWIND(_S_unref(__left))
        }

        void pop_front()
        {
            _RopeRep* __old = _M_tree_ptr;
            _M_tree_ptr = _S_substring(_M_tree_ptr, 1, _M_tree_ptr->_M_size);
            _S_unref(__old);
        }

        _CharT front() const
        {
            return _S_fetch(_M_tree_ptr, 0);
        }

        void balance()
        {
            _RopeRep* __old = _M_tree_ptr;
            _M_tree_ptr = _S_balance(_M_tree_ptr);
            _S_unref(__old);
        }

        void copy(_CharT* __buffer) const {
            destroy(__buffer, __buffer + size());
            _S_flatten(_M_tree_ptr, __buffer);
        }

        // This is the copy function from the standard, but
        // with the arguments reordered to make it consistent with the
        // rest of the interface.
        // Note that this guaranteed not to compile if the draft standard
        // order is assumed.
        size_type copy(size_type __pos, size_type __n, _CharT* __buffer) const 
        {
            size_t __size = size();
            size_t __len = (__pos + __n > __size? __size - __pos : __n);

            destroy(__buffer, __buffer + __len);
            _S_flatten(_M_tree_ptr, __pos, __len, __buffer);
            return __len;
        }

        // Print to stdout, exposing structure.  May be useful for
        // performance debugging.
        void dump() {
            _S_dump(_M_tree_ptr);
        }

        // Convert to 0 terminated string in new allocated memory.
        // Embedded 0s in the input do not terminate the copy.
        const _CharT* c_str() const;

        // As above, but lso use the flattened representation as the
        // the new rope representation.
        const _CharT* replace_with_c_str();

        // Reclaim memory for the c_str generated flattened string.
        // Intentionally undocumented, since it's hard to say when this
        // is safe for multiple threads.
        void delete_c_str () {
            if (0 == _M_tree_ptr) return;
            if (_RopeRep::_S_leaf == _M_tree_ptr->_M_tag && 
                ((_RopeLeaf*)_M_tree_ptr)->_M_data == 
                      _M_tree_ptr->_M_c_string) {
                // Representation shared
                return;
            }
#           ifndef __GC
              _M_tree_ptr->_M_free_c_string();
#           endif
            _M_tree_ptr->_M_c_string = 0;
        }

        _CharT operator[] (size_type __pos) const {
            return _S_fetch(_M_tree_ptr, __pos);
        }

        _CharT at(size_type __pos) const {
           // if (__pos >= size()) throw out_of_range;  // XXX
           return (*this)[__pos];
        }

        const_iterator begin() const {
            return(const_iterator(_M_tree_ptr, 0));
        }

        // An easy way to get a const iterator from a non-const container.
        const_iterator const_begin() const {
            return(const_iterator(_M_tree_ptr, 0));
        }

        const_iterator end() const {
            return(const_iterator(_M_tree_ptr, size()));
        }

        const_iterator const_end() const {
            return(const_iterator(_M_tree_ptr, size()));
        }

        size_type size() const { 
            return(0 == _M_tree_ptr? 0 : _M_tree_ptr->_M_size);
        }

        size_type length() const {
            return size();
        }

        size_type max_size() const {
            return _S_min_len[_RopeRep::_S_max_rope_depth-1] - 1;
            //  Guarantees that the result can be sufficirntly
            //  balanced.  Longer ropes will probably still work,
            //  but it's harder to make guarantees.
        }

        typedef reverse_iterator<const_iterator> const_reverse_iterator;

        const_reverse_iterator rbegin() const {
            return const_reverse_iterator(end());
        }

        const_reverse_iterator const_rbegin() const {
            return const_reverse_iterator(end());
        }

        const_reverse_iterator rend() const {
            return const_reverse_iterator(begin());
        }

        const_reverse_iterator const_rend() const {
            return const_reverse_iterator(begin());
        }

        template<class _CharT2, class _Alloc2>
        friend rope<_CharT2,_Alloc2>
        operator+ (const rope<_CharT2,_Alloc2>& __left,
                   const rope<_CharT2,_Alloc2>& __right);
        
        template<class _CharT2, class _Alloc2>
        friend rope<_CharT2,_Alloc2>
        operator+ (const rope<_CharT2,_Alloc2>& __left,
                   const _CharT2* __right);
        
        template<class _CharT2, class _Alloc2>
        friend rope<_CharT2,_Alloc2>
        operator+ (const rope<_CharT2,_Alloc2>& __left, _CharT2 __right);
        // The symmetric cases are intentionally omitted, since they're presumed
        // to be less common, and we don't handle them as well.

        // The following should really be templatized.
        // The first argument should be an input iterator or
        // forward iterator with value_type _CharT.
        rope& append(const _CharT* __iter, size_t __n) {
            _RopeRep* __result = 
              _S_destr_concat_char_iter(_M_tree_ptr, __iter, __n);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
            return *this;
        }

        rope& append(const _CharT* __c_string) {
            size_t __len = _S_char_ptr_len(__c_string);
            append(__c_string, __len);
            return(*this);
        }

        rope& append(const _CharT* __s, const _CharT* __e) {
            _RopeRep* __result =
                _S_destr_concat_char_iter(_M_tree_ptr, __s, __e - __s);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
            return *this;
        }

        rope& append(const_iterator __s, const_iterator __e) {
            __stl_assert(__s._M_root == __e._M_root);
            __stl_assert(get_allocator() == __s._M_root->get_allocator());
            _Self_destruct_ptr __appendee(_S_substring(
              __s._M_root, __s._M_current_pos, __e._M_current_pos));
            _RopeRep* __result = 
              _S_concat(_M_tree_ptr, (_RopeRep*)__appendee);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
            return *this;
        }

        rope& append(_CharT __c) {
            _RopeRep* __result = 
              _S_destr_concat_char_iter(_M_tree_ptr, &__c, 1);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
            return *this;
        }

        rope& append() { return append(_CharT()); }  // XXX why?

        rope& append(const rope& __y) {
            __stl_assert(__y.get_allocator() == get_allocator());
            _RopeRep* __result = _S_concat(_M_tree_ptr, __y._M_tree_ptr);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
            return *this;
        }

        rope& append(size_t __n, _CharT __c) {
            rope<_CharT,_Alloc> __last(__n, __c);
            return append(__last);
        }

        void swap(rope& __b) {
            __stl_assert(get_allocator() == __b.get_allocator());
            _RopeRep* __tmp = _M_tree_ptr;
            _M_tree_ptr = __b._M_tree_ptr;
            __b._M_tree_ptr = __tmp;
        }


    protected:
        // Result is included in refcount.
        static _RopeRep* replace(_RopeRep* __old, size_t __pos1,
                                  size_t __pos2, _RopeRep* __r) {
            if (0 == __old) { _S_ref(__r); return __r; }
            _Self_destruct_ptr __left(
              _S_substring(__old, 0, __pos1));
            _Self_destruct_ptr __right(
              _S_substring(__old, __pos2, __old->_M_size));
            _RopeRep* __result;

            __stl_assert(__old->get_allocator() == __r->get_allocator());
            if (0 == __r) {
                __result = _S_concat(__left, __right);
            } else {
                _Self_destruct_ptr __left_result(_S_concat(__left, __r));
                __result = _S_concat(__left_result, __right);
            }
            return __result;
        }

    public:
        void insert(size_t __p, const rope& __r) {
            _RopeRep* __result = 
              replace(_M_tree_ptr, __p, __p, __r._M_tree_ptr);
            __stl_assert(get_allocator() == __r.get_allocator());
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
        }

        void insert(size_t __p, size_t __n, _CharT __c) {
            rope<_CharT,_Alloc> __r(__n,__c);
            insert(__p, __r);
        }

        void insert(size_t __p, const _CharT* __i, size_t __n) {
            _Self_destruct_ptr __left(_S_substring(_M_tree_ptr, 0, __p));
            _Self_destruct_ptr __right(_S_substring(_M_tree_ptr, __p, size()));
            _Self_destruct_ptr __left_result(
              _S_concat_char_iter(__left, __i, __n));
                // _S_ destr_concat_char_iter should be safe here.
                // But as it stands it's probably not a win, since __left
                // is likely to have additional references.
            _RopeRep* __result = _S_concat(__left_result, __right);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
        }

        void insert(size_t __p, const _CharT* __c_string) {
            insert(__p, __c_string, _S_char_ptr_len(__c_string));
        }

        void insert(size_t __p, _CharT __c) {
            insert(__p, &__c, 1);
        }

        void insert(size_t __p) {
            _CharT __c = _CharT();
            insert(__p, &__c, 1);
        }

        void insert(size_t __p, const _CharT* __i, const _CharT* __j) {
            rope __r(__i, __j);
            insert(__p, __r);
        }

        void insert(size_t __p, const const_iterator& __i,
                              const const_iterator& __j) {
            rope __r(__i, __j);
            insert(__p, __r);
        }

        void insert(size_t __p, const iterator& __i,
                              const iterator& __j) {
            rope __r(__i, __j);
            insert(__p, __r);
        }

        // (position, length) versions of replace operations:

        void replace(size_t __p, size_t __n, const rope& __r) {
            _RopeRep* __result = 
              replace(_M_tree_ptr, __p, __p + __n, __r._M_tree_ptr);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
        }

        void replace(size_t __p, size_t __n, 
                     const _CharT* __i, size_t __i_len) {
            rope __r(__i, __i_len);
            replace(__p, __n, __r);
        }

        void replace(size_t __p, size_t __n, _CharT __c) {
            rope __r(__c);
            replace(__p, __n, __r);
        }

        void replace(size_t __p, size_t __n, const _CharT* __c_string) {
            rope __r(__c_string);
            replace(__p, __n, __r);
        }

        void replace(size_t __p, size_t __n, 
                     const _CharT* __i, const _CharT* __j) {
            rope __r(__i, __j);
            replace(__p, __n, __r);
        }

        void replace(size_t __p, size_t __n,
                     const const_iterator& __i, const const_iterator& __j) {
            rope __r(__i, __j);
            replace(__p, __n, __r);
        }

        void replace(size_t __p, size_t __n,
                     const iterator& __i, const iterator& __j) {
            rope __r(__i, __j);
            replace(__p, __n, __r);
        }

        // Single character variants:
        void replace(size_t __p, _CharT __c) {
            iterator __i(this, __p);
            *__i = __c;
        }

        void replace(size_t __p, const rope& __r) {
            replace(__p, 1, __r);
        }

        void replace(size_t __p, const _CharT* __i, size_t __i_len) {
            replace(__p, 1, __i, __i_len);
        }

        void replace(size_t __p, const _CharT* __c_string) {
            replace(__p, 1, __c_string);
        }

        void replace(size_t __p, const _CharT* __i, const _CharT* __j) {
            replace(__p, 1, __i, __j);
        }

        void replace(size_t __p, const const_iterator& __i,
                               const const_iterator& __j) {
            replace(__p, 1, __i, __j);
        }

        void replace(size_t __p, const iterator& __i,
                               const iterator& __j) {
            replace(__p, 1, __i, __j);
        }

        // Erase, (position, size) variant.
        void erase(size_t __p, size_t __n) {
            _RopeRep* __result = replace(_M_tree_ptr, __p, __p + __n, 0);
            _S_unref(_M_tree_ptr);
            _M_tree_ptr = __result;
        }

        // Erase, single character
        void erase(size_t __p) {
            erase(__p, __p + 1);
        }

        // Insert, iterator variants.  
        iterator insert(const iterator& __p, const rope& __r)
                { insert(__p.index(), __r); return __p; }
        iterator insert(const iterator& __p, size_t __n, _CharT __c)
                { insert(__p.index(), __n, __c); return __p; }
        iterator insert(const iterator& __p, _CharT __c) 
                { insert(__p.index(), __c); return __p; }
        iterator insert(const iterator& __p ) 
                { insert(__p.index()); return __p; }
        iterator insert(const iterator& __p, const _CharT* c_string) 
                { insert(__p.index(), c_string); return __p; }
        iterator insert(const iterator& __p, const _CharT* __i, size_t __n)
                { insert(__p.index(), __i, __n); return __p; }
        iterator insert(const iterator& __p, const _CharT* __i, 
                        const _CharT* __j)
                { insert(__p.index(), __i, __j);  return __p; }
        iterator insert(const iterator& __p,
                        const const_iterator& __i, const const_iterator& __j)
                { insert(__p.index(), __i, __j); return __p; }
        iterator insert(const iterator& __p,
                        const iterator& __i, const iterator& __j)
                { insert(__p.index(), __i, __j); return __p; }

        // Replace, range variants.
        void replace(const iterator& __p, const iterator& __q,
                     const rope& __r)
                { replace(__p.index(), __q.index() - __p.index(), __r); }
        void replace(const iterator& __p, const iterator& __q, _CharT __c)
                { replace(__p.index(), __q.index() - __p.index(), __c); }
        void replace(const iterator& __p, const iterator& __q,
                     const _CharT* __c_string)
                { replace(__p.index(), __q.index() - __p.index(), __c_string); }
        void replace(const iterator& __p, const iterator& __q,
                     const _CharT* __i, size_t __n)
                { replace(__p.index(), __q.index() - __p.index(), __i, __n); }
        void replace(const iterator& __p, const iterator& __q,
                     const _CharT* __i, const _CharT* __j)
                { replace(__p.index(), __q.index() - __p.index(), __i, __j); }
        void replace(const iterator& __p, const iterator& __q,
                     const const_iterator& __i, const const_iterator& __j)
                { replace(__p.index(), __q.index() - __p.index(), __i, __j); }
        void replace(const iterator& __p, const iterator& __q,
                     const iterator& __i, const iterator& __j)
                { replace(__p.index(), __q.index() - __p.index(), __i, __j); }

        // Replace, iterator variants.
        void replace(const iterator& __p, const rope& __r)
                { replace(__p.index(), __r); }
        void replace(const iterator& __p, _CharT __c)
                { replace(__p.index(), __c); }
        void replace(const iterator& __p, const _CharT* __c_string)
                { replace(__p.index(), __c_string); }
        void replace(const iterator& __p, const _CharT* __i, size_t __n)
                { replace(__p.index(), __i, __n); }
        void replace(const iterator& __p, const _CharT* __i, const _CharT* __j)
                { replace(__p.index(), __i, __j); }
        void replace(const iterator& __p, const_iterator __i, 
                     const_iterator __j)
                { replace(__p.index(), __i, __j); }
        void replace(const iterator& __p, iterator __i, iterator __j)
                { replace(__p.index(), __i, __j); }

        // Iterator and range variants of erase
        iterator erase(const iterator& __p, const iterator& __q) {
            size_t __p_index = __p.index();
            erase(__p_index, __q.index() - __p_index);
            return iterator(this, __p_index);
        }
        iterator erase(const iterator& __p) {
            size_t __p_index = __p.index();
            erase(__p_index, 1);
            return iterator(this, __p_index);
        }

        rope substr(size_t __start, size_t __len = 1) const {
            return rope<_CharT,_Alloc>(
                        _S_substring(_M_tree_ptr, __start, __start + __len));
        }

        rope substr(iterator __start, iterator __end) const {
            return rope<_CharT,_Alloc>(
                _S_substring(_M_tree_ptr, __start.index(), __end.index()));
        }
        
        rope substr(iterator __start) const {
            size_t __pos = __start.index();
            return rope<_CharT,_Alloc>(
                        _S_substring(_M_tree_ptr, __pos, __pos + 1));
        }
        
        rope substr(const_iterator __start, const_iterator __end) const {
            // This might eventually take advantage of the cache in the
            // iterator.
            return rope<_CharT,_Alloc>(
              _S_substring(_M_tree_ptr, __start.index(), __end.index()));
        }

        rope<_CharT,_Alloc> substr(const_iterator __start) {
            size_t __pos = __start.index();
            return rope<_CharT,_Alloc>(
              _S_substring(_M_tree_ptr, __pos, __pos + 1));
        }

        static const size_type npos;

        size_type find(_CharT __c, size_type __pos = 0) const;
        size_type find(const _CharT* __s, size_type __pos = 0) const {
            size_type __result_pos;
            const_iterator __result = search(const_begin() + __pos, const_end(),
                                           __s, __s + _S_char_ptr_len(__s));
            __result_pos = __result.index();
#           ifndef __STL_OLD_ROPE_SEMANTICS
                if (__result_pos == size()) __result_pos = npos;
#           endif
            return __result_pos;
        }

        iterator mutable_begin() {
            return(iterator(this, 0));
        }

        iterator mutable_end() {
            return(iterator(this, size()));
        }

        typedef reverse_iterator<iterator> reverse_iterator;

        reverse_iterator mutable_rbegin() {
            return reverse_iterator(mutable_end());
        }

        reverse_iterator mutable_rend() {
            return reverse_iterator(mutable_begin());
        }

        reference mutable_reference_at(size_type __pos) {
            return reference(this, __pos);
        }

#       ifdef __STD_STUFF
            reference operator[] (size_type __pos) {
                return _char_ref_proxy(this, __pos);
            }

            reference at(size_type __pos) {
                // if (__pos >= size()) throw out_of_range;  // XXX
                return (*this)[__pos];
            }

            void resize(size_type __n, _CharT __c) {}
            void resize(size_type __n) {}
            void reserve(size_type __res_arg = 0) {}
            size_type capacity() const {
                return max_size();
            }

          // Stuff below this line is dangerous because it's error prone.
          // I would really like to get rid of it.
            // copy function with funny arg ordering.
              size_type copy(_CharT* __buffer, size_type __n, 
                             size_type __pos = 0) const {
                return copy(__pos, __n, __buffer);
              }

            iterator end() { return mutable_end(); }

            iterator begin() { return mutable_begin(); }

            reverse_iterator rend() { return mutable_rend(); }

            reverse_iterator rbegin() { return mutable_rbegin(); }

#       else

            const_iterator end() { return const_end(); }

            const_iterator begin() { return const_begin(); }

            const_reverse_iterator rend() { return const_rend(); }
  
            const_reverse_iterator rbegin() { return const_rbegin(); }

#       endif
        
};

template <class _CharT, class _Alloc>
const rope<_CharT, _Alloc>::size_type rope<_CharT, _Alloc>::npos =
                        (size_type)(-1);

template <class _CharT, class _Alloc>
inline bool operator== (const _Rope_const_iterator<_CharT,_Alloc>& __x,
                        const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return (__x._M_current_pos == __y._M_current_pos && 
          __x._M_root == __y._M_root);
}

template <class _CharT, class _Alloc>
inline bool operator< (const _Rope_const_iterator<_CharT,_Alloc>& __x,
                       const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return (__x._M_current_pos < __y._M_current_pos);
}

template <class _CharT, class _Alloc>
inline bool operator!= (const _Rope_const_iterator<_CharT,_Alloc>& __x,
                        const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return !(__x == __y);
}

template <class _CharT, class _Alloc>
inline bool operator> (const _Rope_const_iterator<_CharT,_Alloc>& __x,
                       const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return __y < __x;
}

template <class _CharT, class _Alloc>
inline bool operator<= (const _Rope_const_iterator<_CharT,_Alloc>& __x,
                        const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return !(__y < __x);
}

template <class _CharT, class _Alloc>
inline bool operator>= (const _Rope_const_iterator<_CharT,_Alloc>& __x,
                        const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return !(__x < __y);
}

template <class _CharT, class _Alloc>
inline ptrdiff_t operator-(const _Rope_const_iterator<_CharT,_Alloc>& __x,
                           const _Rope_const_iterator<_CharT,_Alloc>& __y) {
  return (ptrdiff_t)__x._M_current_pos - (ptrdiff_t)__y._M_current_pos;
}

template <class _CharT, class _Alloc>
inline _Rope_const_iterator<_CharT,_Alloc>
operator-(const _Rope_const_iterator<_CharT,_Alloc>& __x, ptrdiff_t __n) {
  return _Rope_const_iterator<_CharT,_Alloc>(
            __x._M_root, __x._M_current_pos - __n);
}

template <class _CharT, class _Alloc>
inline _Rope_const_iterator<_CharT,_Alloc>
operator+(const _Rope_const_iterator<_CharT,_Alloc>& __x, ptrdiff_t __n) {
  return _Rope_const_iterator<_CharT,_Alloc>(
           __x._M_root, __x._M_current_pos + __n);
}

template <class _CharT, class _Alloc>
inline _Rope_const_iterator<_CharT,_Alloc>
operator+(ptrdiff_t __n, const _Rope_const_iterator<_CharT,_Alloc>& __x) {
  return _Rope_const_iterator<_CharT,_Alloc>(
           __x._M_root, __x._M_current_pos + __n);
}

template <class _CharT, class _Alloc>
inline bool operator== (const _Rope_iterator<_CharT,_Alloc>& __x,
                        const _Rope_iterator<_CharT,_Alloc>& __y) {
  return (__x._M_current_pos == __y._M_current_pos && 
          __x._M_root_rope == __y._M_root_rope);
}

template <class _CharT, class _Alloc>
inline bool operator< (const _Rope_iterator<_CharT,_Alloc>& __x,
                       const _Rope_iterator<_CharT,_Alloc>& __y) {
  return (__x._M_current_pos < __y._M_current_pos);
}

template <class _CharT, class _Alloc>
inline bool operator!= (const _Rope_iterator<_CharT,_Alloc>& __x,
                        const _Rope_iterator<_CharT,_Alloc>& __y) {
  return !(__x == __y);
}

template <class _CharT, class _Alloc>
inline bool operator> (const _Rope_iterator<_CharT,_Alloc>& __x,
                       const _Rope_iterator<_CharT,_Alloc>& __y) {
  return __y < __x;
}

template <class _CharT, class _Alloc>
inline bool operator<= (const _Rope_iterator<_CharT,_Alloc>& __x,
                        const _Rope_iterator<_CharT,_Alloc>& __y) {
  return !(__y < __x);
}

template <class _CharT, class _Alloc>
inline bool operator>= (const _Rope_iterator<_CharT,_Alloc>& __x,
                        const _Rope_iterator<_CharT,_Alloc>& __y) {
  return !(__x < __y);
}

template <class _CharT, class _Alloc>
inline ptrdiff_t operator-(const _Rope_iterator<_CharT,_Alloc>& __x,
                           const _Rope_iterator<_CharT,_Alloc>& __y) {
  return (ptrdiff_t)__x._M_current_pos - (ptrdiff_t)__y._M_current_pos;
}

template <class _CharT, class _Alloc>
inline _Rope_iterator<_CharT,_Alloc>
operator-(const _Rope_iterator<_CharT,_Alloc>& __x,
          ptrdiff_t __n) {
  return _Rope_iterator<_CharT,_Alloc>(
    __x._M_root_rope, __x._M_current_pos - __n);
}

template <class _CharT, class _Alloc>
inline _Rope_iterator<_CharT,_Alloc>
operator+(const _Rope_iterator<_CharT,_Alloc>& __x,
          ptrdiff_t __n) {
  return _Rope_iterator<_CharT,_Alloc>(
    __x._M_root_rope, __x._M_current_pos + __n);
}

template <class _CharT, class _Alloc>
inline _Rope_iterator<_CharT,_Alloc>
operator+(ptrdiff_t __n, const _Rope_iterator<_CharT,_Alloc>& __x) {
  return _Rope_iterator<_CharT,_Alloc>(
    __x._M_root_rope, __x._M_current_pos + __n);
}

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>
operator+ (const rope<_CharT,_Alloc>& __left,
           const rope<_CharT,_Alloc>& __right)
{
    __stl_assert(__left.get_allocator() == __right.get_allocator());
    return rope<_CharT,_Alloc>(
      rope<_CharT,_Alloc>::_S_concat(__left._M_tree_ptr, __right._M_tree_ptr));
    // Inlining this should make it possible to keep __left and
    // __right in registers.
}

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>&
operator+= (rope<_CharT,_Alloc>& __left, 
      const rope<_CharT,_Alloc>& __right)
{
    __left.append(__right);
    return __left;
}

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>
operator+ (const rope<_CharT,_Alloc>& __left,
           const _CharT* __right) {
    size_t __rlen = rope<_CharT,_Alloc>::_S_char_ptr_len(__right);
    return rope<_CharT,_Alloc>(
      rope<_CharT,_Alloc>::_S_concat_char_iter(
        __left._M_tree_ptr, __right, __rlen)); 
}

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>&
operator+= (rope<_CharT,_Alloc>& __left,
            const _CharT* __right) {
    __left.append(__right);
    return __left;
}

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>
operator+ (const rope<_CharT,_Alloc>& __left, _CharT __right) {
    return rope<_CharT,_Alloc>(
      rope<_CharT,_Alloc>::_S_concat_char_iter(
        __left._M_tree_ptr, &__right, 1));
}

template <class _CharT, class _Alloc>
inline
rope<_CharT,_Alloc>&
operator+= (rope<_CharT,_Alloc>& __left, _CharT __right) {
    __left.append(__right);
    return __left;
}

template <class _CharT, class _Alloc>
bool
operator< (const rope<_CharT,_Alloc>& __left, 
           const rope<_CharT,_Alloc>& __right) {
    return __left.compare(__right) < 0;
}
        
template <class _CharT, class _Alloc>
bool
operator== (const rope<_CharT,_Alloc>& __left, 
            const rope<_CharT,_Alloc>& __right) {
    return __left.compare(__right) == 0;
}

template <class _CharT, class _Alloc>
inline bool operator== (const _Rope_char_ptr_proxy<_CharT,_Alloc>& __x,
                        const _Rope_char_ptr_proxy<_CharT,_Alloc>& __y) {
        return (__x._M_pos == __y._M_pos && __x._M_root == __y._M_root);
}

template <class _CharT, class _Alloc>
inline bool
operator!= (const rope<_CharT,_Alloc>& __x, const rope<_CharT,_Alloc>& __y) {
  return !(__x == __y);
}

template <class _CharT, class _Alloc>
inline bool
operator> (const rope<_CharT,_Alloc>& __x, const rope<_CharT,_Alloc>& __y) {
  return __y < __x;
}

template <class _CharT, class _Alloc>
inline bool
operator<= (const rope<_CharT,_Alloc>& __x, const rope<_CharT,_Alloc>& __y) {
  return !(__y < __x);
}

template <class _CharT, class _Alloc>
inline bool
operator>= (const rope<_CharT,_Alloc>& __x, const rope<_CharT,_Alloc>& __y) {
  return !(__x < __y);
}

template <class _CharT, class _Alloc>
inline bool operator!= (const _Rope_char_ptr_proxy<_CharT,_Alloc>& __x,
                        const _Rope_char_ptr_proxy<_CharT,_Alloc>& __y) {
  return !(__x == __y);
}

template<class _CharT, class _Traits, class _Alloc>
basic_ostream<_CharT, _Traits>& operator<<
                                        (basic_ostream<_CharT, _Traits>& __o,
                                         const rope<_CharT, _Alloc>& __r);

typedef rope<char> crope;
typedef rope<wchar_t> wrope;

inline crope::reference __mutable_reference_at(crope& __c, size_t __i)
{
    return __c.mutable_reference_at(__i);
}

inline wrope::reference __mutable_reference_at(wrope& __c, size_t __i)
{
    return __c.mutable_reference_at(__i);
}

template <class _CharT, class _Alloc>
inline void swap(rope<_CharT,_Alloc>& __x, rope<_CharT,_Alloc>& __y) {
  __x.swap(__y);
}

// Hash functions should probably be revisited later:
template<> struct hash<crope>
{
  size_t operator()(const crope& __str) const
  {
    size_t __size = __str.size();

    if (0 == __size) return 0;
    return 13*__str[0] + 5*__str[__size - 1] + __size;
  }
};


template<> struct hash<wrope>
{
  size_t operator()(const wrope& __str) const
  {
    size_t __size = __str.size();

    if (0 == __size) return 0;
    return 13*__str[0] + 5*__str[__size - 1] + __size;
  }
};

} // namespace std

# include <ext/ropeimpl.h>

# endif /* __SGI_STL_INTERNAL_ROPE_H */

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