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Using std::is_constructible in the constraints introduces a spurious dependency on the type being destructible, which should not be required for constructing with an allocator. The test case shows a case where the type has a private destructor, which can be destroyed by the allocator, but std::is_destructible and std::is_constructible are false. Similarly, using is_nothrow_constructible in the noexcept-specifiers for the construct members of allocator_traits and std::allocator, __gnu_cxx::__new_allocator, and __gnu_cxx::__malloc_allocator gives the wrong answer if the type isn't destructible. We need a new type trait to define those correctly, so that we only check if the placement new-expression is nothrow after using is_constructible to check that it would be well-formed. Instead of just fixing the overly restrictive constraint to check for placement new, rewrite allocator_traits in terms of 'if constexpr' using variable templates and the detection idiom. Although we can use 'if constexpr' and variable templates in C++11 with appropriate uses of diagnostic pragmas, we can't have constexpr functions with multiple return statements. This means that in C++11 mode the _S_nothrow_construct and _S_nothrow_destroy helpers used for noexcept-specifiers still need to be overlaods using enable_if. Nearly everything else can be simplified to reduce overload resolution and enable_if checks. libstdc++-v3/ChangeLog: PR libstdc++/108619 * include/bits/alloc_traits.h (__allocator_traits_base): Add variable templates for detecting which allocator operations are supported. (allocator_traits): Use 'if constexpr' instead of dispatching to overloads constrained with enable_if. (allocator_traits<allocator<T>>::construct): Use Construct if construct_at is not supported. Use __is_nothrow_new_constructible for noexcept-specifier. (allocator_traits<allocator<void>>::construct): Use __is_nothrow_new_constructible for noexcept-specifier. * include/bits/new_allocator.h (construct): Likewise. * include/ext/malloc_allocator.h (construct): Likewise. * include/std/type_traits (__is_nothrow_new_constructible): New variable template. * testsuite/20_util/allocator/89510.cc: Adjust expected results. * testsuite/ext/malloc_allocator/89510.cc: Likewise. * testsuite/ext/new_allocator/89510.cc: Likewise. * testsuite/20_util/allocator_traits/members/108619.cc: New test. |
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.. | ||
89510.cc | ||
check_allocate_max_size.cc | ||
check_deallocate_null.cc | ||
check_delete.cc | ||
check_new.cc | ||
deallocate_global.cc | ||
deallocate_local.cc | ||
eq.cc | ||
explicit_instantiation.cc | ||
overaligned.cc | ||
sanity.cc | ||
variadic_construct.cc |