Because uses-allocator construction is invariably done with a const
lvalue the __uses_alloc helper should use a const lvalue for the
is_constructible checks. Otherwise, it can detect that the type can be
constructed from an rvalue, and then an error happens when a const
lvalue is passed to the constructor instead.
Prior to LWG DR 2586 scoped_allocator_adaptor incorrectly used an rvalue
type in the is_constructible check and then used a non-const lvalue for
the actual construction. The other components using uses-allocator
construction (tuple and polymorphic_allocator) have always done so with
a const lvalue allocator, although the use of __use_alloc in our
implementation meant they behaved the same as scoped_allocator_adaptor
and incorrectly used rvalues for the is_constructible checks.
In C++20 the P0591R4 changes mean that all uses-allocator construction
is defined in terms of the new uses_allocator_construction_args
functions, which always use a const lvalue allocator.
The changes in this patch ensure that the __use_alloc helper correctly
matches the requirements in the standard, consistently using a const
lvalue allocator for the is_constructible checks and the actual
constructor arguments.
* doc/xml/manual/intro.xml: Document LWG 2586 status.
* include/bits/uses_allocator.h (__uses_alloc): Use const lvalue
allocator type in is_constructible checks.
* testsuite/20_util/scoped_allocator/69293_neg.cc: Adjust dg-error.
* testsuite/20_util/scoped_allocator/dr2586.cc: New test.
* testsuite/20_util/tuple/cons/allocators.cc: Add test using
problematic type from LWG 2586 discussion.
* testsuite/20_util/uses_allocator/69293_neg.cc: Adjust dg-error.
* testsuite/20_util/uses_allocator/cons_neg.cc: Likewise.
From-SVN: r268882
Remove duplicated logic in experimental::pmr::polymorphic_allocator by
calling the __uses_allocator_construct helper.
Fix bugs in std::pmr::polymorphic_allocator with incorrect SFINAE
constraint and incorrect argument order.
* include/bits/uses_allocator.h (__uses_allocator_construct): Qualify
calls to __uses_allocator_construct_impl and __use_alloc.
* include/experimental/memory_resource
(polymorphic_allocator::_M_construct): Remove.
(polymorphic_allocator::construct): Call __uses_allocator_construct.
Qualify calls to __use_alloc.
* include/std/memory_resource (polymorphic_allocator::construct): Fix
type in SFINAE constraint. Use constexpr if instead of tag dispatching
to _S_construct overloads.
(polymorphic_allocator::construct(pair<T1, T2>*, ...)): Fix order of
arguments to _S_construct_p.
(polymorphic_allocator::_S_construct): Remove.
(polymorphic_allocator::_S_construct_p): Return allocators by value
not by reference.
* include/std/scoped_allocator (scoped_allocator_adaptor::construct):
Qualify calls to __use_alloc.
* testsuite/20_util/polymorphic_allocator/construct_pair.cc: New test,
copied from testsuite/20_util/scoped_allocator/construct_pair.cc.
* testsuite/experimental/polymorphic_allocator/1.cc: New test.
* testsuite/experimental/polymorphic_allocator/construct_pair.cc:
New test.
From-SVN: r263566
The erased_type condition is only true for code using the Library
Fundamentals TS, so assume it's less common and only check it after
checking for convertibility.
This does mean for types using erased_type the more expensive
convertibility check is done first, but such types are rare.
* include/bits/uses_allocator.h (__is_erased_or_convertible): Reorder
conditions. Add comments.
* testsuite/20_util/uses_allocator/69293_neg.cc: Adjust dg-error line.
* testsuite/20_util/uses_allocator/cons_neg.cc: Likewise.
* testsuite/20_util/scoped_allocator/69293_neg.cc: Likewise.
From-SVN: r262945
* include/bits/uses_allocator.h (__use_alloc(const _Alloc&&)): Add
deleted overload to prevent dangling references to rvalues.
* include/experimental/memory_resource
(polymorphic_allocator::construct): Do not call __use_alloc with
rvalue arguments.
From-SVN: r250019
* include/bits/uses_allocator.h (__is_uses_allocator_constructible_v)
(__is_nothrow_uses_allocator_constructible_v): Only define for C++14
and later.
From-SVN: r241301
* include/Makefile.am: Add new file std/variant.
* include/Makefile.in: Generated from Makefile.am.
* include/bits/enable_special_members.h: Add a tag type to allow
the construction in non-default constructor.
* include/bits/uses_allocator.h: Add convenience traits to
detect constructibility.
* include/std/variant: Implement <variant>.
* testsuite/20_util/variant/compile.cc: Compile-time tests.
* testsuite/20_util/variant/run.cc: Runtime tests.
From-SVN: r239590
