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[libc++][NFC] Use if constexpr instead of SFINAE to simplify shared_ptr #113495

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[libc++][NFC] Use if constexpr instead of SFINAE to simplify shared_ptr #113495

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[libc++][NFC] Use `if constexpr` instead of SFINAE to simplify shared…
ldionne Sep 14, 2023
97c42fe
Fix obvious typo
ldionne Oct 24, 2024
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47 changes: 18 additions & 29 deletions libcxx/include/__memory/shared_ptr.h
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Original file line number Diff line number Diff line change
Expand Up @@ -252,45 +252,34 @@ template <class _Tp, class _Alloc>
struct __shared_ptr_emplace : __shared_weak_count {
using __value_type = __remove_cv_t<_Tp>;

template <class... _Args,
class _Allocator = _Alloc,
__enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
static_assert(
sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
::new (static_cast<void*>(__get_elem())) __value_type;
}

template <class... _Args,
class _Allocator = _Alloc,
__enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
template <class... _Args>
_LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __value_type>::type;
_TpAlloc __tmp(*__get_alloc());
allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
if constexpr (is_same<typename _Alloc::value_type, __for_overwrite_tag>::value) {
static_assert(
sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
::new (static_cast<void*>(__get_elem())) __value_type;
} else {
using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __value_type>::type;
_TpAlloc __tmp(*__get_alloc());
allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
}
}

_LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }

_LIBCPP_HIDE_FROM_ABI __value_type* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }

private:
template <class _Allocator = _Alloc,
__enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
__get_elem()->~__value_type();
}

template <class _Allocator = _Alloc,
__enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
using _TpAlloc = typename __allocator_traits_rebind<_Allocator, __remove_cv_t<_Tp> >::type;
_TpAlloc __tmp(*__get_alloc());
allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
_LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
if constexpr (is_same<typename _Alloc::value_type, __for_overwrite_tag>::value) {
__get_elem()->~__value_type();
} else {
using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __remove_cv_t<_Tp> >::type;
_TpAlloc __tmp(*__get_alloc());
allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
}
}

_LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __on_zero_shared_impl(); }

_LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
using _ControlBlockAlloc = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
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