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libstdc++: Define converting assignment operator for std::move_iterator

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As clarified by LWG 3265, std::move_iterator is supposed to have an
assignment operator that converts from a different specialization of
std::move_iterator, which performs an assignment. That has always been
missing from libstdc++, so assigning a different type actually performs
a converting construction, then an assignment. This is non-conforming
for the (fairly contrived) case where the converting assignment is
well-formed but the converting construction is not.

	* include/bits/stl_iterator.h (move_iterator::operator=): Define.
	* testsuite/24_iterators/move_iterator/dr3265.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-06-09 22:16:24 +01:00
parent d364705791
commit 733167f9d5
2 changed files with 59 additions and 0 deletions
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8
libstdc++-v3/include/bits/stl_iterator.h
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@ -1307,6 +1307,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
move_iterator(const move_iterator<_Iter>& __i)
: _M_current(__i.base()) { }
template<typename _Iter>
_GLIBCXX17_CONSTEXPR
move_iterator& operator=(const move_iterator<_Iter>& __i)
{
_M_current = __i.base();
return *this;
}
#if __cplusplus <= 201703L
_GLIBCXX17_CONSTEXPR iterator_type
base() const

51
libstdc++-v3/testsuite/24_iterators/move_iterator/dr3265.cc Normal file
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@ -0,0 +1,51 @@
// Copyright (C) 2020 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 3, 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 COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// { dg-do compile { target c++11 } }
#include <iterator>
struct Iter
{
using iterator_category = std::forward_iterator_tag;
using value_type = int;
using pointer = int*;
using reference = int&;
using difference_type = std::ptrdiff_t;
Iter();
// Construction from int* is not valid:
Iter(int*) = delete;
// Assignment from int* is valid:
Iter& operator=(int*);
Iter& operator++();
Iter operator++(int);
int& operator*() const;
int* operator->() const;
template<int N> friend bool operator==(Iter, Iter);
};
void test01()
{
std::move_iterator<Iter> m;
int i = 0;
m = std::make_move_iterator(&i); // Should use assignment not construction
}