On Thu, 15 May 2025, Tomasz Kamiński wrote:
> This patch implements C++26 function_ref as specified in P0792R14,
> with correction for constraints for constructor accepting nontype_t
> parameter from LWG 4256.
>
> As function_ref may store a pointer to the const object, __Ptrs::_M_obj is
> changed to const void*, so again we do not cast away const from const
> objects. To help with necessary casts, a __polyfunc::__cast_to helper is
> added, that accepts reference to or target type direclty.
>
> The _Invoker now defines additional call methods used by function_ref:
> _S_ptrs() for invoking target passed by reference, and __S_nttp, _S_bind_ptr,
> _S_bind_ref for handling constructors accepting nontype_t. The existing
> _S_call_storage is changed to thin wrapper, that initialies _Ptrs, and
> forwards
> to _S_call_ptrs.
>
> This reduced the most uses of _Storage::_M_ptr and _Storage::_M_ref,
> so this functions was removed, and _Manager uses were adjusted.
>
> Finally we make function_ref available in freestanding mode, as
> move_only_function and copyable_function are currently only available in
> hosted,
> so we define _Manager and _Mo_base only if either __glibcxx_move_only_function
> or __glibcxx_copyable_function is defined.
>
> PR libstdc++/119126
>
> libstdc++-v3/ChangeLog:
>
> * doc/doxygen/stdheader.cc: Added funcref_impl.h file.
> * include/Makefile.am: Added funcref_impl.h file.
> * include/Makefile.in: Added funcref_impl.h file.
> * include/bits/funcref_impl.h: New file.
> * include/bits/funcwrap.h: (_Ptrs::_M_obj): Const-qualify.
> (_Storage::_M_ptr, _Storage::_M_ref): Remove.
> (__polyfunc::__cast_to) Define.
> (_Base_invoker::_S_ptrs, _Base_invoker::_S_nttp)
> (_Base_invoker::_S_bind_ptrs, _Base_invoker::_S_bind_ref)
> (_Base_invoker::_S_call_ptrs): Define.
> (_Base_invoker::_S_call_storage): Foward to _S_call_ptrs.
> (_Manager::_S_local, _Manager::_S_ptr): Adjust for _M_obj being
> const qualified.
> (__polyfunc::_Manager, __polyfunc::_Mo_base): Guard with
> __glibcxx_move_only_function || __glibcxx_copyable_function.
> (__polyfunc::__skip_first_arg, __polyfunc::__deduce_funcref)
> (std::function_ref) [__glibcxx_function_ref]: Define.
> * include/bits/utility.h (std::nontype_t, std::nontype)
> (__is_nontype_v) [__glibcxx_function_ref]: Define.
> * include/bits/version.def: Define function_ref.
> * include/bits/version.h: Regenerate.
> * include/std/functional: Define __cpp_lib_function_ref.
> * src/c++23/std.cc.in (std::nontype_t, std::nontype)
> (std::function_ref) [__cpp_lib_function_ref]: Export.
> * testsuite/20_util/function_ref/assign.cc: New test.
> * testsuite/20_util/function_ref/call.cc: New test.
> * testsuite/20_util/function_ref/cons.cc: New test.
> * testsuite/20_util/function_ref/cons_neg.cc: New test.
> * testsuite/20_util/function_ref/conv.cc: New test.
> * testsuite/20_util/function_ref/deduction.cc: New test.
> ---
> This patch handles using nontype with function pointer/reference.
> In function_ref we now use _M_init(ptr) function, that handles
> both function and object pointers. The __polyfunc::__cast_to is
> also expaned to handle function_types.
>
> libstdc++-v3/doc/doxygen/stdheader.cc | 1 +
> libstdc++-v3/include/Makefile.am | 1 +
> libstdc++-v3/include/Makefile.in | 1 +
> libstdc++-v3/include/bits/funcref_impl.h | 198 ++++++++++++++++
> libstdc++-v3/include/bits/funcwrap.h | 185 +++++++++++----
> libstdc++-v3/include/bits/utility.h | 17 ++
> libstdc++-v3/include/bits/version.def | 8 +
> libstdc++-v3/include/bits/version.h | 10 +
> libstdc++-v3/include/std/functional | 3 +-
> libstdc++-v3/src/c++23/std.cc.in | 7 +
> .../testsuite/20_util/function_ref/assign.cc | 108 +++++++++
> .../testsuite/20_util/function_ref/call.cc | 186 +++++++++++++++
> .../testsuite/20_util/function_ref/cons.cc | 218 ++++++++++++++++++
> .../20_util/function_ref/cons_neg.cc | 30 +++
> .../testsuite/20_util/function_ref/conv.cc | 152 ++++++++++++
> .../20_util/function_ref/deduction.cc | 103 +++++++++
> 16 files changed, 1181 insertions(+), 47 deletions(-)
> create mode 100644 libstdc++-v3/include/bits/funcref_impl.h
> create mode 100644 libstdc++-v3/testsuite/20_util/function_ref/assign.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/function_ref/call.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/function_ref/conv.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
>
> diff --git a/libstdc++-v3/doc/doxygen/stdheader.cc
> b/libstdc++-v3/doc/doxygen/stdheader.cc
> index 839bfc81bc0..938b2b04a26 100644
> --- a/libstdc++-v3/doc/doxygen/stdheader.cc
> +++ b/libstdc++-v3/doc/doxygen/stdheader.cc
> @@ -55,6 +55,7 @@ void init_map()
> headers["functional_hash.h"] = "functional";
> headers["mofunc_impl.h"] = "functional";
> headers["cpyfunc_impl.h"] = "functional";
> + headers["funcref_impl.h"] = "functional";
> headers["funcwrap.h"] = "functional";
> headers["invoke.h"] = "functional";
> headers["ranges_cmp.h"] = "functional";
> diff --git a/libstdc++-v3/include/Makefile.am
> b/libstdc++-v3/include/Makefile.am
> index 3e5b6c4142e..baf0290d655 100644
> --- a/libstdc++-v3/include/Makefile.am
> +++ b/libstdc++-v3/include/Makefile.am
> @@ -205,6 +205,7 @@ bits_headers = \
> ${bits_srcdir}/fs_ops.h \
> ${bits_srcdir}/fs_path.h \
> ${bits_srcdir}/fstream.tcc \
> + ${bits_srcdir}/funcref_impl.h \
> ${bits_srcdir}/funcwrap.h \
> ${bits_srcdir}/gslice.h \
> ${bits_srcdir}/gslice_array.h \
> diff --git a/libstdc++-v3/include/Makefile.in
> b/libstdc++-v3/include/Makefile.in
> index 3531162b5f7..e4e1079d8bd 100644
> --- a/libstdc++-v3/include/Makefile.in
> +++ b/libstdc++-v3/include/Makefile.in
> @@ -559,6 +559,7 @@ bits_freestanding = \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/fs_path.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/fstream.tcc \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/funcwrap.h \
> +@GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/funcref_impl.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/gslice.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/gslice_array.h \
> @GLIBCXX_HOSTED_TRUE@ ${bits_srcdir}/hashtable.h \
> diff --git a/libstdc++-v3/include/bits/funcref_impl.h
> b/libstdc++-v3/include/bits/funcref_impl.h
> new file mode 100644
> index 00000000000..7be5060acf7
> --- /dev/null
> +++ b/libstdc++-v3/include/bits/funcref_impl.h
> @@ -0,0 +1,198 @@
> +// Implementation of std::function_ref -*- C++ -*-
> +
> +// Copyright The GNU Toolchain Authors.
> +//
> +// 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.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/bits/funcref_impl.h
> + * This is an internal header file, included by other library headers.
> + * Do not attempt to use it directly. @headername{functional}
> + */
> +
> +#ifndef _GLIBCXX_MOF_CV
> +# define _GLIBCXX_MOF_CV
> +#endif
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> + /// @cond undocumented
> + namespace __polyfunc
> + {
> + template<bool _Noex, typename _Ret, typename _Class, typename... _Args>
> + struct __skip_first_arg<_Ret(_Class::*)(_Args...) _GLIBCXX_MOF_CV
> + noexcept(_Noex)>
> + { using type = _Ret(_Args...) noexcept(_Noex); };
> +
> + template<bool _Noex, typename _Ret, typename _Class, typename... _Args>
> + struct __skip_first_arg<_Ret(_Class::*)(_Args...) _GLIBCXX_MOF_CV&
> + noexcept(_Noex)>
> + { using type = _Ret(_Args...) noexcept(_Noex); };
> + } // namespace __polyfunc
> + /// @endcond
> +
> + /**
> + * @brief Non-owning polymorphic function wrapper.
> + * @ingroup functors
> + * @since C++26
> + * @headerfile functional
> + *
> + * The `std::function_ref` class template is a non-owning call wrapper,
> + * that refers a bound object. Using function_ref outside of lifetime
> + * of bound object has undefined behavior.
> + *
> + * It supports const-qualification and no-throw guarantees. The
> qualifications and
> + * exception-specification of the signature are respected when when
> invoking the
> + * reference function.
> + */
> + template<typename _Res, typename... _ArgTypes, bool _Noex>
> + class function_ref<_Res(_ArgTypes...) _GLIBCXX_MOF_CV
> + noexcept(_Noex)>
> + {
> + using _Invoker = __polyfunc::_Invoker<_Noex, _Res, _ArgTypes...>;
> + using _Signature = _Invoker::_Signature;
> +
> + // [func.wrap.ref.ctor]/1 is-invokable-using
> + template<typename... _Tps>
> + static constexpr bool __is_invocable_using
> + = __conditional_t<_Noex,
> + is_nothrow_invocable_r<_Res, _Tps..., _ArgTypes...>,
> + is_invocable_r<_Res, _Tps..., _ArgTypes...>>::value;
> +
> + public:
> + /// Target and bound object is function pointed by parameter.
> + template<typename _Fn>
> + requires is_function_v<_Fn> && __is_invocable_using<_Fn*>
> + function_ref(_Fn* __fn) noexcept
> + {
> + __glibcxx_assert(__fn != nullptr);
> + this->_M_invoke = _Invoker::template _S_ptrs<_Fn*>();
All these explicit 'this->' seem unnecessary/inconsistent?
> + this->_M_init(__fn);
> + }
> +
> + /// Target and bound object is object referenced by parameter.
> + template<typename _Fn, typename _Vt = remove_reference_t<_Fn>>
> + requires (!is_same_v<remove_cv_t<_Vt>, function_ref>)
> + && (!is_member_pointer_v<_Vt>)
> + // We deviate from standard by having this condition, that forces
> + // function references to use _Fn* constructors. This simplies
> + // implementation and provide better diagnostic when used in
> + // constant expression (above constructor is not constexpr).
> + && (!is_function_v<_Vt>)
> + && __is_invocable_using<_Vt _GLIBCXX_MOF_CV&>
> + constexpr
> + function_ref(_Fn&& __f) noexcept
> + {
> + this->_M_invoke = _Invoker::template _S_ptrs<_Vt _GLIBCXX_MOF_CV&>();
> + this->_M_init(std::addressof(__f));
> + }
> +
> + // _GLIBCXX_RESOLVE_LIB_DEFECTS
> + // 4256. Incorrect constrains for function_ref constructors from
> nontype
> + /// Target object is __fn. There is no bound object.
> + template<auto __fn>
> + requires __is_invocable_using<const decltype(__fn)&>
> + constexpr
> + function_ref(nontype_t<__fn>) noexcept
> + {
> + using _Fn = remove_cv_t<decltype(__fn)>;
> + if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>)
> + static_assert(__fn != nullptr);
> +
> + this->_M_invoke = &_Invoker::template _S_nttp<__fn>;
> + this->_M_ptrs._M_obj = nullptr;
> + }
> +
> + /// Target object is equivalent to
> std::bind_front<_fn>(std::ref(__ref)).
> + /// Bound object is object referenced by second parameter.
> + template<auto __fn, typename _Up, typename _Td =
> remove_reference_t<_Up>>
> + requires (!is_rvalue_reference_v<_Up&&>)
> + && __is_invocable_using<const decltype(__fn)&, _Td _GLIBCXX_MOF_CV&>
> + constexpr
> + function_ref(nontype_t<__fn>, _Up&& __ref) noexcept
> + {
> + using _Fn = remove_cv_t<decltype(__fn)>;
> + if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>)
> + static_assert(__fn != nullptr);
> +
> + using _Tr = _Td _GLIBCXX_MOF_CV&;
> + if constexpr (is_member_pointer_v<_Fn> && is_lvalue_reference_v<_Tr>)
> + // N.B. invoking member pointer on lvalue produces the same effects,
> + // as invoking it on pointer to that lvalue.
> + this->_M_invoke = &_Invoker::template _S_bind_ptr<__fn, _Td
> _GLIBCXX_MOF_CV>;
> + else
> + this->_M_invoke = &_Invoker::template _S_bind_ref<__fn, _Tr>;
> + this->_M_init(std::addressof(__ref));
> + }
> +
> + /// Target object is equivalent to std::bind_front<_fn>(__ptr).
> + /// Bound object is object pointed by second parameter (if any).
> + template<auto __fn, typename _Td>
> + requires __is_invocable_using<const decltype(__fn)&, _Td
> _GLIBCXX_MOF_CV*>
> + constexpr
> + function_ref(nontype_t<__fn>, _Td _GLIBCXX_MOF_CV* __ptr) noexcept
> + {
> + using _Fn = remove_cv_t<decltype(__fn)>;
> + if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>)
> + static_assert(__fn != nullptr);
> + if constexpr (is_member_pointer_v<_Fn>)
> + __glibcxx_assert(__ptr != nullptr);
> +
> + this->_M_invoke = &_Invoker::template _S_bind_ptr<__fn, _Td
> _GLIBCXX_MOF_CV>;
> + this->_M_init(__ptr);
> + }
> +
> + template<typename _Tp>
> + requires (!is_same_v<_Tp, function_ref>)
> + && (!is_pointer_v<_Tp>) && (!__is_nontype_v<_Tp>)
> + function_ref&
> + operator=(_Tp) = delete;
> +
> + /** Invoke the target object.
> + *
> + * The bound object will be invoked using the supplied arguments,
> + * and as const or non-const, as dictated by the template arguments
> + * of the `function_ref` specialization.
> + */
> + _Res
> + operator()(_ArgTypes... __args) const noexcept(_Noex)
> + { return _M_invoke(this->_M_ptrs, std::forward<_ArgTypes>(__args)...);
> }
> +
> + private:
> + template<typename _Tp>
> + constexpr void
> + _M_init(_Tp* __ptr) noexcept
> + {
> + if constexpr (is_function_v<_Tp>)
> + _M_ptrs._M_func = reinterpret_cast<void(*)()>(__ptr);
> + else
> + _M_ptrs._M_obj = __ptr;
> + }
> +
> + typename _Invoker::__ptrs_func_t _M_invoke;
> + __polyfunc::_Ptrs _M_ptrs;
> + };
> +
> +#undef _GLIBCXX_MOF_CV
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace std
> diff --git a/libstdc++-v3/include/bits/funcwrap.h
> b/libstdc++-v3/include/bits/funcwrap.h
> index 4e053534cf5..639b910afb2 100644
> --- a/libstdc++-v3/include/bits/funcwrap.h
> +++ b/libstdc++-v3/include/bits/funcwrap.h
> @@ -1,4 +1,5 @@
> -// Implementation of std::move_only_function and std::copyable_function -*-
> C++ -*-
> +// Implementation of std::move_only_function, std::copyable_function
> +// and std::function_ref -*- C++ -*-
>
> // Copyright The GNU Toolchain Authors.
> //
> @@ -36,7 +37,7 @@
>
> #include <bits/version.h>
>
> -#if defined(__glibcxx_move_only_function) ||
> defined(__glibcxx_copyable_function)
> +#if __glibcxx_move_only_function || __glibcxx_copyable_function ||
> __glibcxx_function_ref
>
> #include <bits/invoke.h>
> #include <bits/utility.h>
> @@ -53,10 +54,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> {
> union _Ptrs
> {
> - void* _M_obj;
> + const void* _M_obj;
> void (*_M_func)();
> };
>
> + template<typename _Tp>
> + [[__gnu__::__always_inline__]]
> + constexpr auto*
> + __cast_to(_Ptrs __ptrs) noexcept
> + {
> + using _Td = remove_reference_t<_Tp>;
> + if constexpr (is_function_v<_Td>)
> + return reinterpret_cast<_Td*>(__ptrs._M_func);
> + else if constexpr (is_const_v<_Td>)
> + return static_cast<_Td*>(__ptrs._M_obj);
> + else
> + return static_cast<_Td*>(const_cast<void*>(__ptrs._M_obj));
> + }
> +
> struct _Storage
> {
> void* _M_addr() noexcept { return &_M_bytes[0]; }
> @@ -97,32 +112,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> ::new (_M_addr()) _Tp(std::forward<_Args>(__args)...);
> }
>
> - template<typename _Tp>
> - [[__gnu__::__always_inline__]]
> - _Tp*
> - _M_ptr() const noexcept
> - {
> - if constexpr (!_S_stored_locally<remove_const_t<_Tp>>())
> - return static_cast<_Tp*>(_M_ptrs._M_obj);
> - else if constexpr (is_const_v<_Tp>)
> - return static_cast<_Tp*>(_M_addr());
> - else
> - // _Manager and _Invoker pass _Storage by const&, even for mutable
> sources.
> - return static_cast<_Tp*>(const_cast<void*>(_M_addr()));
> - }
> -
> - template<typename _Ref>
> - [[__gnu__::__always_inline__]]
> - _Ref
> - _M_ref() const noexcept
> - {
> - using _Tp = remove_reference_t<_Ref>;
> - if constexpr (is_function_v<remove_pointer_t<_Tp>>)
> - return reinterpret_cast<_Tp>(_M_ptrs._M_func);
> - else
> - return static_cast<_Ref>(*_M_ptr<_Tp>());
> - }
> -
> // We want to have enough space to store a simple delegate type.
> struct _Delegate { void (_Storage::*__pfm)(); _Storage* __obj; };
> union {
> @@ -143,6 +132,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> _S_storage()
> { return &_S_call_storage<_Adjust_target<_Tp>>; }
>
> + using __ptrs_func_t = _Ret(*)(_Ptrs, _Args...) noexcept(_Noex);
> + template<typename _Tp>
> + static consteval __ptrs_func_t
> + _S_ptrs()
> + { return &_S_call_ptrs<_Adjust_target<_Tp>>; }
> +
> +#ifdef __glibcxx_function_ref // C++ >= 26
> + template<auto __fn>
> + static _Ret
> + _S_nttp(_Ptrs, _Args... __args) noexcept(_Noex)
> + { return std::__invoke_r<_Ret>(__fn, std::forward<_Args>(__args)...); }
> +
> + template<auto __fn, typename _Tp>
> + static _Ret
> + _S_bind_ptr(_Ptrs __ptrs, _Args... __args) noexcept(_Noex)
> + {
> + auto __p = __polyfunc::__cast_to<_Tp>(__ptrs);
I guess we can use auto* here and in the other __cast_to call sites for
more clarity.
> + return std::__invoke_r<_Ret>(__fn, __p,
> std::forward<_Args>(__args)...);
> + }
> +
> + template<auto __fn, typename _Ref>
> + static _Ret
> + _S_bind_ref(_Ptrs __ptrs, _Args... __args) noexcept(_Noex)
> + {
> + auto __p = __polyfunc::__cast_to<_Ref>(__ptrs);
> + return std::__invoke_r<_Ret>(__fn, static_cast<_Ref>(*__p),
> + std::forward<_Args>(__args)...);
> + }
> +#endif // __glibcxx_function_ref
> +
> private:
> template<typename _Tp, typename _Td = remove_cvref_t<_Tp>>
> using _Adjust_target =
> @@ -152,8 +171,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> static _Ret
> _S_call_storage(const _Storage& __ref, _Args... __args) noexcept(_Noex)
> {
> - return std::__invoke_r<_Ret>(__ref._M_ref<_Tp>(),
> - std::forward<_Args>(__args)...);
> + _Ptrs __ptrs;
> + if constexpr (is_function_v<remove_pointer_t<_Tp>>)
> + __ptrs._M_func = __ref._M_ptrs._M_func;
> + else if constexpr
> (!_Storage::_S_stored_locally<remove_cvref_t<_Tp>>())
> + __ptrs._M_obj = __ref._M_ptrs._M_obj;
> + else
> + __ptrs._M_obj = __ref._M_addr();
> + return _S_call_ptrs<_Tp>(__ptrs, std::forward<_Args>(__args)...);
> + }
> +
> + template<typename _Tp>
> + static _Ret
> + _S_call_ptrs(_Ptrs __ptrs, _Args... __args) noexcept(_Noex)
> + {
> + if constexpr (is_function_v<remove_pointer_t<_Tp>>)
> + return std::__invoke_r<_Ret>(reinterpret_cast<_Tp>(__ptrs._M_func),
> + std::forward<_Args>(__args)...);
> + else
> + {
> + auto __p = __polyfunc::__cast_to<_Tp>(__ptrs);
> + return std::__invoke_r<_Ret>(static_cast<_Tp>(*__p),
> + std::forward<_Args>(__args)...);
> + }
> }
> };
>
> @@ -184,6 +224,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> return false;
> }
>
> +#if __glibcxx_move_only_function || __glibcxx_copyable_function
> struct _Manager
> {
> enum class _Op
> @@ -241,7 +282,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> switch (__op)
> {
> case _Op::_Address:
> - __target._M_ptrs._M_obj = const_cast<void*>(__src->_M_addr());
> + __target._M_ptrs._M_obj = __src->_M_addr();
> return;
> case _Op::_Move:
> case _Op::_Copy:
> @@ -263,24 +304,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> switch (__op)
> {
> case _Op::_Address:
> - __target._M_ptrs._M_obj = __src->_M_ptr<_Tp>();
> + __target._M_ptrs._M_obj = __src->_M_addr();
> return;
> case _Op::_Move:
> {
> - _Tp* __obj = __src->_M_ptr<_Tp>();
> + _Tp* __obj =
> static_cast<_Tp*>(const_cast<void*>(__src->_M_addr()));
> ::new(__target._M_addr()) _Tp(std::move(*__obj));
> __obj->~_Tp();
> }
> return;
> case _Op::_Destroy:
> - __target._M_ptr<_Tp>()->~_Tp();
> + static_cast<_Tp*>(__target._M_addr())->~_Tp();
> return;
> case _Op::_Copy:
> if constexpr (_Provide_copy)
> - ::new (__target._M_addr()) _Tp(__src->_M_ref<const _Tp&>());
> - else
> - __builtin_unreachable();
> - return;
> + {
> + auto* __obj = static_cast<const _Tp*>(__src->_M_addr());
> + ::new (__target._M_addr()) _Tp(*__obj);
> + return;
> + }
> + __builtin_unreachable();
> }
> }
>
> @@ -296,14 +339,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> __target._M_ptrs._M_obj = __src->_M_ptrs._M_obj;
> return;
> case _Op::_Destroy:
> - delete __target._M_ptr<_Tp>();
> + delete static_cast<const _Tp*>(__target._M_ptrs._M_obj);
> return;
> case _Op::_Copy:
> if constexpr (_Provide_copy)
> - __target._M_ptrs._M_obj = new _Tp(__src->_M_ref<const _Tp&>());
> - else
> - __builtin_unreachable();
> - return;
> + {
> + auto* __obj = static_cast<const _Tp*>(__src->_M_ptrs._M_obj);
> + __target._M_ptrs._M_obj = new _Tp(*__obj);
> + return;
> + }
> + __builtin_unreachable();
> }
> }
> };
> @@ -382,7 +427,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> friend class _Cpy_base;
> #endif // __glibcxx_copyable_function
> };
> -
> +#endif // __glibcxx_copyable_function || __glibcxx_copyable_function
> } // namespace __polyfunc
> /// @endcond
>
> @@ -468,6 +513,48 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> } // namespace __detail::__variant
> #endif // __glibcxx_copyable_function
>
> +#ifdef __glibcxx_function_ref // C++ >= 26
> + /// @cond undocumented
> + namespace __polyfunc
> + {
> + template<typename _Sig>
> + struct __skip_first_arg;
> +
> + template<bool _Noex, typename _Ret, typename _Arg, typename... _Args>
> + struct __skip_first_arg<_Ret(*)(_Arg, _Args...) noexcept(_Noex)>
> + { using type = _Ret(_Args...) noexcept(_Noex); };
Can you add a comment that the other partial specializations are defined
in funcref_impl.h?
> +
> + template<typename _Fn, typename _Tr>
> + consteval auto __deduce_funcref()
Missing newline. LGTM besides that.
> + {
> + if constexpr (is_member_object_pointer_v<_Fn>)
> + // TODO Consider reporting issue to make this noexcept
> + return static_cast<invoke_result_t<_Fn, _Tr>(*)()>(nullptr);
> + else
> + return static_cast<__skip_first_arg<_Fn>::type*>(nullptr);
> + }
> + } // namespace __polyfunc
> + /// @endcond
> +
> + template<typename... _Signature>
> + class function_ref; // not defined
> +
> + template<typename _Fn>
> + requires is_function_v<_Fn>
> + function_ref(_Fn*) -> function_ref<_Fn>;
> +
> + template<auto __f, class _Fn = remove_pointer_t<decltype(__f)>>
> + requires is_function_v<_Fn>
> + function_ref(nontype_t<__f>) -> function_ref<_Fn>;
> +
> + template<auto __f, typename _Tp, class _Fn = decltype(__f)>
> + requires is_member_pointer_v<_Fn> || is_function_v<remove_pointer_t<_Fn>>
> + function_ref(nontype_t<__f>, _Tp&&)
> + -> function_ref<
> + remove_pointer_t<decltype(__polyfunc::__deduce_funcref<_Fn,
> _Tp&>())>>;
> +
> +#endif // __glibcxx_function_ref
> +
> _GLIBCXX_END_NAMESPACE_VERSION
> } // namespace std
>
> @@ -503,5 +590,11 @@ _GLIBCXX_END_NAMESPACE_VERSION
> #include "cpyfunc_impl.h"
> #endif // __glibcxx_copyable_function
>
> -#endif // __glibcxx_copyable_function || __glibcxx_copyable_function
> +#ifdef __glibcxx_function_ref // C++ >= 26
> +#include "funcref_impl.h"
> +#define _GLIBCXX_MOF_CV const
> +#include "funcref_impl.h"
> +#endif // __glibcxx_function_ref
> +
> +#endif // move_only_function || copyable_function || function_ref
> #endif // _GLIBCXX_FUNCWRAP_H
> diff --git a/libstdc++-v3/include/bits/utility.h
> b/libstdc++-v3/include/bits/utility.h
> index 6fa6b679c6d..84d25e0c658 100644
> --- a/libstdc++-v3/include/bits/utility.h
> +++ b/libstdc++-v3/include/bits/utility.h
> @@ -316,6 +316,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> inline constexpr sorted_equivalent_t sorted_equivalent{};
> #endif
>
> +#if __glibcxx_function_ref // >= C++26
> + template<auto>
> + struct nontype_t
> + {
> + explicit nontype_t() = default;
> + };
> +
> + template<auto __val>
> + constexpr nontype_t<__val> nontype{};
> +
> + template<typename>
> + inline constexpr bool __is_nontype_v = false;
> +
> + template<auto __val>
> + inline constexpr bool __is_nontype_v<nontype_t<__val>> = true;
> +#endif
> +
> _GLIBCXX_END_NAMESPACE_VERSION
> } // namespace
>
> diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> index 6ca148f0488..55aab40d9bf 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -1756,6 +1756,14 @@ ftms = {
> };
> };
>
> +ftms = {
> + name = function_ref;
> + values = {
> + v = 202306;
> + cxxmin = 26;
> + };
> +};
> +
> ftms = {
> name = out_ptr;
> values = {
> diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> index 48a090c14a3..026c9959482 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -1958,6 +1958,16 @@
> #endif /* !defined(__cpp_lib_copyable_function) &&
> defined(__glibcxx_want_copyable_function) */
> #undef __glibcxx_want_copyable_function
>
> +#if !defined(__cpp_lib_function_ref)
> +# if (__cplusplus > 202302L)
> +# define __glibcxx_function_ref 202306L
> +# if defined(__glibcxx_want_all) || defined(__glibcxx_want_function_ref)
> +# define __cpp_lib_function_ref 202306L
> +# endif
> +# endif
> +#endif /* !defined(__cpp_lib_function_ref) &&
> defined(__glibcxx_want_function_ref) */
> +#undef __glibcxx_want_function_ref
> +
> #if !defined(__cpp_lib_out_ptr)
> # if (__cplusplus >= 202100L)
> # define __glibcxx_out_ptr 202311L
> diff --git a/libstdc++-v3/include/std/functional
> b/libstdc++-v3/include/std/functional
> index 9a55b181e6d..307bcb95bcc 100644
> --- a/libstdc++-v3/include/std/functional
> +++ b/libstdc++-v3/include/std/functional
> @@ -57,6 +57,7 @@
> #define __glibcxx_want_bind_back
> #define __glibcxx_want_constexpr_functional
> #define __glibcxx_want_copyable_function
> +#define __glibcxx_want_function_ref
> #define __glibcxx_want_invoke
> #define __glibcxx_want_invoke_r
> #define __glibcxx_want_move_only_function
> @@ -86,7 +87,7 @@
> # include <bits/ranges_cmp.h> // std::identity, ranges::equal_to etc.
> # include <compare>
> #endif
> -#if defined(__glibcxx_move_only_function) ||
> defined(__glibcxx_copyable_function)
> +#if __glibcxx_move_only_function || __glibcxx_copyable_function ||
> __glibcxx_function_ref
> # include <bits/funcwrap.h>
> #endif
>
> diff --git a/libstdc++-v3/src/c++23/std.cc.in
> b/libstdc++-v3/src/c++23/std.cc.in
> index 417c8a1a562..ba468530338 100644
> --- a/libstdc++-v3/src/c++23/std.cc.in
> +++ b/libstdc++-v3/src/c++23/std.cc.in
> @@ -1414,6 +1414,9 @@ export namespace std
> #endif
> #if __cpp_lib_copyable_function
> using std::copyable_function;
> +#endif
> +#if __cpp_lib_function_ref
> + using std::function_ref;
> #endif
> using std::multiplies;
> using std::negate;
> @@ -3195,6 +3198,10 @@ export namespace std
> using std::make_integer_sequence;
> using std::move;
> using std::move_if_noexcept;
> +#if __cpp_lib_function_ref
> + using std::nontype_t;
> + using std::nontype;
> +#endif
> using std::pair;
> using std::swap;
> using std::operator==;
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/assign.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/assign.cc
> new file mode 100644
> index 00000000000..9b02dc49c2a
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/assign.cc
> @@ -0,0 +1,108 @@
> +// { dg-do compile { target c++26 } }
> +
> +#include <functional>
> +
> +#ifndef __cpp_lib_function_ref
> +# error "Feature-test macro for function_ref missing in <functional>"
> +#elif __cpp_lib_function_ref != 202306L
> +# error "Feature-test macro for function_ref has wrong value in <functional>"
> +#endif
> +
> +using std::nontype;
> +using std::nontype_t;
> +using std::function_ref;
> +
> +using std::is_nothrow_move_assignable_v;
> +using std::is_nothrow_copy_assignable_v;
> +using std::is_nothrow_assignable_v;
> +using std::is_assignable_v;
> +using std::is_nothrow_swappable_v;
> +using std::is_trivially_copyable_v;
> +
> +static_assert( is_nothrow_move_assignable_v<function_ref<void()>> );
> +static_assert( is_nothrow_copy_assignable_v<function_ref<void()>> );
> +static_assert( is_nothrow_swappable_v<function_ref<void()>> );
> +
> +static_assert( ! is_assignable_v<function_ref<void()>, std::nullptr_t> );
> +
> +static_assert( is_nothrow_assignable_v<function_ref<void()>, void()> );
> +static_assert( is_nothrow_assignable_v<function_ref<void()>, void(&)()> );
> +static_assert( is_nothrow_assignable_v<function_ref<void()>, void(*)()> );
> +static_assert( is_nothrow_assignable_v<function_ref<void()>, int()> );
> +static_assert( is_nothrow_assignable_v<function_ref<void()>, int(&)()> );
> +static_assert( is_nothrow_assignable_v<function_ref<void()>, int(*)()> );
> +static_assert( ! is_nothrow_assignable_v<function_ref<void()>, void(int)> );
> +static_assert( is_nothrow_assignable_v<function_ref<void(int)>, void(int)> );
> +
> +static_assert( is_nothrow_assignable_v<function_ref<void()>,
> + void() noexcept> );
> +static_assert( is_nothrow_assignable_v<function_ref<void() noexcept>,
> + void() noexcept> );
> +static_assert( ! is_assignable_v<function_ref<void() noexcept>, void() > );
> +
> +struct S
> +{
> + int x;
> + int f();
> +};
> +int funS(S);
> +
> +static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> + decltype(funS)> );
> +static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> + decltype(&funS)> );
> +static_assert( ! is_assignable_v<function_ref<int(S)>, decltype(&S::x)> );
> +static_assert( ! is_assignable_v<function_ref<int(S)>, decltype(&S::f)> );
> +
> +static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> + nontype_t<funS>> );
> +static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> + nontype_t<&funS>> );
> +static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> + nontype_t<&S::x>> );
> +static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> + nontype_t<&S::f>> );
> +struct Q
> +{
> + void operator()() const;
> +};
> +
> +static_assert( ! is_assignable_v<function_ref<void()>, Q> );
> +static_assert( ! is_assignable_v<function_ref<void()>, Q&> );
> +static_assert( ! is_assignable_v<function_ref<void()>, const Q&> );
> +static_assert( ! is_assignable_v<function_ref<void() const>, Q> );
> +static_assert( ! is_assignable_v<function_ref<void() const>, Q&> );
> +static_assert( ! is_assignable_v<function_ref<void() const>, const Q&> );
> +
> +static_assert( is_nothrow_assignable_v<function_ref<void()>,
> + nontype_t<Q{}>> );
> +static_assert( is_nothrow_assignable_v<function_ref<void() const>,
> + nontype_t<Q{}>> );
> +
> +constexpr bool
> +test_constexpr()
> +{
> + function_ref<void(S)> fp(nontype<funS>);
> + fp = nontype<funS>;
> + fp = nontype<&funS>;
> + fp = nontype<&S::x>;
> + fp = nontype<&S::f>;
> +
> + constexpr Q cq;
> + function_ref<void() const> fq(cq);
> + fq = nontype<cq>;
> + return true;
> +}
> +static_assert( test_constexpr() );
> +
> +void func();
> +
> +void
> +test_instantiation()
> +{
> + function_ref<void(S)> fp(funS);
> + fp = funS;
> + fp = &funS;
> +
> + test_constexpr();
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> new file mode 100644
> index 00000000000..a91c6b4abb9
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> @@ -0,0 +1,186 @@
> +// { dg-do run { target c++26 } }
> +
> +#include <functional>
> +#include <utility>
> +#include <testsuite_hooks.h>
> +
> +using std::nontype;
> +using std::function_ref;
> +
> +using std::is_same_v;
> +using std::is_invocable_v;
> +using std::is_nothrow_invocable_v;
> +using std::invoke_result_t;
> +
> +// Check return types
> +static_assert( is_same_v<void, invoke_result_t<function_ref<void()>>> );
> +static_assert( is_same_v<int, invoke_result_t<function_ref<int()>>> );
> +static_assert( is_same_v<int&, invoke_result_t<function_ref<int&()>>> );
> +
> +// Const qualier applies to target object
> +static_assert( is_invocable_v< function_ref<void()> const > );
> +static_assert( is_invocable_v< function_ref<void()> const &> );
> +static_assert( is_invocable_v< function_ref<void() const> > );
> +static_assert( is_invocable_v< function_ref<void() const> &> );
> +static_assert( is_invocable_v< function_ref<void() const> const > );
> +static_assert( is_invocable_v< function_ref<void() const> const &> );
> +
> +// With noexcept-specifier
> +static_assert( ! is_nothrow_invocable_v< function_ref<void()> > );
> +static_assert( ! is_nothrow_invocable_v< function_ref<void()
> noexcept(false)> > );
> +static_assert( is_nothrow_invocable_v< function_ref<void() noexcept> > );
> +
> +void
> +test01()
> +{
> + struct F
> + {
> + int operator()() { return 0; }
> + int operator()() const { return 1; }
> + };
> +
> + function_ref<int()> f0{F{}};
> + VERIFY( f0() == 0 );
> + VERIFY( std::move(f0)() == 0 );
> +
> + function_ref<int()> f1{nontype<F{}>};
> + VERIFY( f1() == 1 );
> + VERIFY( std::move(f1)() == 1 );
> +
> + function_ref<int() const> f2{F{}};
> + VERIFY( f2() == 1 );
> + VERIFY( std::as_const(f2)() == 1 );
> + VERIFY( std::move(f2)() == 1 );
> + VERIFY( std::move(std::as_const(f2))() == 1 );
> +
> + function_ref<int() const> f3{nontype<F{}>};
> + VERIFY( f3() == 1 );
> + VERIFY( std::as_const(f3)() == 1 );
> + VERIFY( std::move(f3)() == 1 );
> + VERIFY( std::move(std::as_const(f3))() == 1 );
> +}
> +
> +void
> +test02()
> +{
> + struct F
> + {
> + struct Arg {};
> + int operator()(Arg& arg) const { return 0; }
> + int operator()(const Arg& arg) const { return 1; }
> + };
> + F::Arg arg;
> +
> + function_ref<int()> f0{std::nontype<F{}>, arg};
> + VERIFY( f0() == 0 );
> + VERIFY( std::move(f0)() == 0 );
> +
> + function_ref<int() const> f1{std::nontype<F{}>, arg};
> + VERIFY( f1() == 1 );
> + VERIFY( std::as_const(f1)() == 1 );
> +}
> +
> +void
> +test03()
> +{
> + struct F
> + {
> + struct Arg {};
> + int operator()(Arg* arg) const { return 0; }
> + int operator()(const Arg* arg) const { return 1; }
> + };
> + F::Arg arg;
> +
> + function_ref<int()> f0{std::nontype<F{}>, &arg};
> + VERIFY( f0() == 0 );
> + VERIFY( std::move(f0)() == 0 );
> +
> + function_ref<int() const> f1{std::nontype<F{}>, &arg};
> + VERIFY( f1() == 1 );
> + VERIFY( std::as_const(f1)() == 1 );
> +}
> +
> +void
> +test04()
> +{
> + constexpr int (*fp)() = [] { return 0; };
> + function_ref<int()> f0{fp};
> + VERIFY( f0() == 0 );
> + VERIFY( std::move(f0)() == 0 );
> +
> + function_ref<int()> f1{nontype<fp>};
> + VERIFY( f1() == 0 );
> + VERIFY( std::move(f1)() == 0 );
> +
> + const function_ref<int() const> f2{fp};
> + VERIFY( f2() == 0 );
> + VERIFY( std::move(f2)() == 0 );
> +
> + const function_ref<int() const> f3{nontype<fp>};
> + VERIFY( f2() == 0 );
> + VERIFY( std::move(f2)() == 0 );
> +}
> +
> +using ftype = int(int);
> +int twice(int x) { return x * 2; }
> +int cube(int x) { return x * x * x; }
> +int callback_ptr(ftype* f, int x) { return f(x); }
> +int callback_ref(ftype& f, int x) { return f(x); }
> +
> +void
> +test05()
> +{
> +
> + function_ref<int(int)> r1(nontype<&callback_ptr>, &twice);
> + VERIFY( r1(2) == 4 );
> + function_ref<int(int)> r2(nontype<&callback_ptr>, cube);
> + VERIFY( r2(2) == 8 );
> +
> + function_ref<int(int)> r3(nontype<&callback_ref>, twice);
> + VERIFY( r3(3) == 6 );
> + function_ref<int(int)> r4(nontype<&callback_ref>, cube);
> + VERIFY( r4(3) == 27 );
> +
> + // Checks if distinction between reference and pointer
> + // is preserved.
> + struct F
> + {
> + static
> + int operator()(ftype* f, int x)
> + { return f(x) + 1000; }
> +
> + static
> + int operator()(ftype& f, int x)
> + { return f(x) + 2000; }
> + };
> + function_ref<int(int)> r5(nontype<F{}>, &twice);
> + VERIFY( r5(2) == 1004 );
> + function_ref<int(int)> r6(nontype<F{}>, twice);
> + VERIFY( r6(2) == 2008 );
> + function_ref<int(int)> r7(nontype<F{}>, &cube);
> + VERIFY( r7(3) == 1006 );
> + function_ref<int(int)> r8(nontype<F{}>, cube);
> + VERIFY( r8(3) == 2027 );
> +}
> +
> +struct Incomplete;
> +
> +void
> +test_params()
> +{
> + auto f = [](auto&&) {};
> + // There is discussion if this is supported.
> + // std::function_ref<void(Incomplete)> f1(f);
> + std::function_ref<void(Incomplete&)> f2(f);
> + // See PR120259, this should be supported.
> + // std::function_ref<void(Incomplete&&)> f3(f);
> +}
> +
> +int main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> + test_params();
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> new file mode 100644
> index 00000000000..a91f5ba3dab
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> @@ -0,0 +1,218 @@
> +// { dg-do compile { target c++26 } }
> +// { dg-add-options no_pch }
> +
> +#include <functional>
> +
> +#ifndef __cpp_lib_function_ref
> +# error "Feature-test macro for function_ref missing in <functional>"
> +#elif __cpp_lib_function_ref != 202306L
> +# error "Feature-test macro for function_ref has wrong value in <functional>"
> +#endif
> +
> +using std::nontype;
> +using std::nontype_t;
> +using std::function_ref;
> +
> +using std::is_default_constructible_v;
> +using std::is_nothrow_copy_constructible_v;
> +using std::is_nothrow_move_constructible_v;
> +using std::is_nothrow_constructible_v;
> +using std::is_constructible_v;
> +using std::is_trivially_copyable_v;
> +
> +static_assert( ! is_default_constructible_v<function_ref<void()>> );
> +static_assert( is_nothrow_move_constructible_v<function_ref<void()>> );
> +static_assert( is_nothrow_copy_constructible_v<function_ref<void()>> );
> +static_assert( is_trivially_copyable_v<function_ref<void()>> );
> +
> +static_assert( ! is_constructible_v<function_ref<void()>, std::nullptr_t> );
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, void()> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, void(&)()> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, void(*)()> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, int()> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, int(&)()> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, int(*)()> );
> +static_assert( ! is_constructible_v<function_ref<void()>, void(int)> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int)>,
> void(int)> );
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void()>,
> + void() noexcept> );
> +static_assert( is_nothrow_constructible_v<function_ref<void() noexcept>,
> + void() noexcept> );
> +static_assert( ! is_constructible_v<function_ref<void() noexcept>,
> + void() > );
> +
> +struct S
> +{
> + int x;
> + int f();
> +};
> +int funS(S);
> +
> +static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> + decltype(funS)> );
> +static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> + decltype(&funS)> );
> +static_assert( ! is_constructible_v<function_ref<int(S)>,
> + decltype(&S::x)> );
> +static_assert( ! is_constructible_v<function_ref<int(S)>,
> + decltype(&S::f)> );
> +
> +static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> + nontype_t<funS>> );
> +static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> + nontype_t<&funS>> );
> +static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> + nontype_t<&S::x>> );
> +static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> + nontype_t<&S::f>> );
> +
> +static_assert( is_nothrow_constructible_v<function_ref<int()>,
> + nontype_t<funS>, S&> );
> +static_assert( is_nothrow_constructible_v<function_ref<int()>,
> + nontype_t<&funS>, S&> );
> +static_assert( is_nothrow_constructible_v<function_ref<int()>,
> + nontype_t<&S::x>, S&> );
> +static_assert( is_nothrow_constructible_v<function_ref<int()>,
> + nontype_t<&S::f>, S&> );
> +
> +static_assert( ! is_constructible_v<function_ref<int()>,
> + nontype_t<funS>, S*> );
> +static_assert( ! is_constructible_v<function_ref<int()>,
> + nontype_t<&funS>, S*> );
> +static_assert( is_nothrow_constructible_v<function_ref<int()>,
> + nontype_t<&S::x>, S*> );
> +static_assert( is_nothrow_constructible_v<function_ref<int()>,
> + nontype_t<&S::f>, S*> );
> +
> +struct M
> +{
> + void operator()();
> +};
> +
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, M> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, M&> );
> +static_assert( ! is_constructible_v<function_ref<void()>, const M&> );
> +static_assert( ! is_constructible_v<function_ref<void() const>, M> );
> +static_assert( ! is_constructible_v<function_ref<void() const>, const M&> );
> +static_assert( ! is_constructible_v<function_ref<void()>,
> + nontype_t<M{}>> );
> +static_assert( ! is_constructible_v<function_ref<void() const>,
> + nontype_t<M{}>> );
> +struct Q
> +{
> + void operator()(int) const;
> + void operator()(int*) const;
> +};
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void(int)>, Q> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int)>, Q&> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int)>, const Q&>
> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int) const>, Q>
> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int) const>, Q&>
> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int) const>,
> const Q&> );
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void(int)>,
> + nontype_t<Q{}>> );
> +static_assert( is_nothrow_constructible_v<function_ref<void(int) const>,
> + nontype_t<Q{}>> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>,
> + nontype_t<Q{}>, int&> );
> +static_assert( is_nothrow_constructible_v<function_ref<void() const>,
> + nontype_t<Q{}>, int&> );
> +static_assert( ! is_constructible_v<function_ref<void()>,
> + nontype_t<Q{}>, int> );
> +static_assert( ! is_constructible_v<function_ref<void() const>,
> + nontype_t<Q{}>, int> );
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void()>,
> + nontype_t<Q{}>, int*> );
> +static_assert( ! is_constructible_v<function_ref<void() const>,
> + nontype_t<Q{}>, int*> );
> +
> +struct L
> +{
> + void operator()() &;
> +};
> +
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, L> );
> +static_assert( is_nothrow_constructible_v<function_ref<void()>, L&> );
> +static_assert( ! is_constructible_v<function_ref<void()>, const L&> );
> +static_assert( ! is_constructible_v<function_ref<void() const>, L> );
> +static_assert( ! is_constructible_v<function_ref<void() const>, const L&> );
> +static_assert( ! is_constructible_v<function_ref<void()>,
> + nontype_t<L{}>> );
> +static_assert( ! is_constructible_v<function_ref<void() const>,
> + nontype_t<L{}>> );
> +
> +struct R
> +{
> + void operator()(float) const&&;
> +};
> +
> +static_assert( ! is_constructible_v<function_ref<void(float)>, R> );
> +static_assert( ! is_constructible_v<function_ref<void(float)>, R&> );
> +static_assert( ! is_constructible_v<function_ref<void(float) const>, R> );
> +static_assert( ! is_constructible_v<function_ref<void(float) const>, R&> );
> +static_assert( ! is_constructible_v<function_ref<void(float) const>, const
> R&> );
> +
> +static_assert( ! is_constructible_v<function_ref<void(float)>,
> + nontype_t<R{}>> );
> +static_assert( ! is_constructible_v<function_ref<void(float) const>,
> + nontype_t<R{}>> );
> +
> +constexpr bool
> +test_constexpr()
> +{
> + function_ref<void(S)> fp1(nontype<funS>);
> + function_ref<void(S)> fp3(nontype<&funS>);
> + function_ref<void(S)> fp4(nontype<&S::x>);
> + function_ref<void(S)> fp5(nontype<&S::f>);
> +
> + S s;
> + function_ref<void()> fp6(nontype<&funS>, s);
> + function_ref<void()> fp7(nontype<&S::x>, s);
> + function_ref<void()> fp8(nontype<&S::x>, &s);
> + function_ref<void()> fp9(nontype<&S::f>, s);
> + function_ref<void()> fp10(nontype<&S::f>, &s);
> +
> + M m;
> + function_ref<void()> fm1(m);
> + function_ref<void()> fm2(std::move(m));
> +
> + Q q;
> + constexpr Q cq;
> + function_ref<void(int)> fq1(q);
> + function_ref<void(int) const> fq2(q);
> + function_ref<void(int) const> fq3(std::move(q));
> +
> + function_ref<void(int)> fcq1(cq);
> + function_ref<void(int) const> f(cq);
> + function_ref<void(int)> fcq3(nontype<cq>);
> + function_ref<void(int) const> fcq4(nontype<cq>);
> +
> + int i = 0;
> + function_ref<void()> fcq5(nontype<cq>, i);
> + function_ref<void() const> fcq6(nontype<cq>, i);
> + function_ref<void()> fcq7(nontype<cq>, &i);
> +
> + L l;
> + function_ref<void()> fl1(l);
> + function_ref<void()> fl2(std::move(l));
> +
> + return true;
> +}
> +static_assert( test_constexpr() );
> +
> +void func();
> +
> +void
> +test_instantiation()
> +{
> + function_ref<void(S)> fp1(funS);
> + function_ref<void(S)> fp2(&funS);
> +
> + test_constexpr();
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> new file mode 100644
> index 00000000000..050090df370
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> @@ -0,0 +1,30 @@
> +// { dg-do compile { target c++26 } }
> +
> +#include <functional>
> +
> +using std::nontype;
> +using std::function_ref;
> +
> +struct S
> +{
> + int x;
> + void foo();
> +};
> +S s;
> +
> +constexpr int(*fp)(S) = nullptr;
> +constexpr int S::*mdp = nullptr;
> +constexpr int (S::*mfp)() = nullptr;
> +
> +function_ref<int(S)> fd1(nontype<fp>); // { dg-error "from here" }
> +function_ref<int(S)> fd2(nontype<mdp>); // { dg-error "from here" }
> +function_ref<int(S)> fd3(nontype<mfp>); // { dg-error "from here" }
> +
> +function_ref<int()> br4(nontype<fp>, s); // { dg-error "from here" }
> +function_ref<int()> br5(nontype<mdp>, s); // { dg-error "from here" }
> +function_ref<int()> br6(nontype<mfp>, s); // { dg-error "from here" }
> +
> +function_ref<int()> bp7(nontype<mdp>, &s); // { dg-error "from here" }
> +function_ref<int()> bp8(nontype<mfp>, &s); // { dg-error "from here" }
> +
> +// { dg-prune-output "static assertion failed" }
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/conv.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/conv.cc
> new file mode 100644
> index 00000000000..49ff0a78829
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/conv.cc
> @@ -0,0 +1,152 @@
> +// { dg-do run { target c++26 } }
> +// { dg-require-effective-target hosted }
> +
> +#include <functional>
> +#include <testsuite_hooks.h>
> +
> +using std::function_ref;
> +
> +static_assert( std::is_constructible_v<std::function_ref<void() const>,
> + std::function_ref<void()>> );
> +
> +// Non-trivial args, guarantess that type is not passed by copy
> +struct CountedArg
> +{
> + CountedArg() = default;
> + CountedArg(const CountedArg& f) noexcept : counter(f.counter) { ++counter;
> }
> + CountedArg& operator=(CountedArg&&) = delete;
> +
> + int counter = 0;
> +};
> +CountedArg const c;
> +
> +// The C++26 [func.wrap.general] p2 does not currently cover funciton_ref,
> +// so we make extra copies of arguments.
> +
> +void
> +test01()
> +{
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::function_ref<int(CountedArg) const noexcept> r1(f);
> + std::move_only_function<int(CountedArg) const noexcept> m1(f);
> + std::copyable_function<int(CountedArg) const noexcept> c1(f);
> +
> + // Complatible signatures
> + std::function_ref<int(CountedArg) const noexcept> r2m(m1);
> + VERIFY( r2m(c) == 2 );
> + std::function_ref<int(CountedArg) const noexcept> r2c(c1);
> + VERIFY( r2c(c) == 2 );
> +
> + std::function_ref<int(CountedArg) const> r3r(r1);
> + VERIFY( r3r(c) == 2 );
> + std::function_ref<int(CountedArg) const> r3m(m1);
> + VERIFY( r3m(c) == 2 );
> + std::function_ref<int(CountedArg) const> r3c(c1);
> + VERIFY( r3c(c) == 2 );
> +
> + std::function_ref<int(CountedArg)> r4r(r1);
> + VERIFY( r4r(c) == 2 );
> + std::function_ref<int(CountedArg)> r4m(m1);
> + VERIFY( r4m(c) == 2 );
> + std::function_ref<int(CountedArg)> r4c(c1);
> + VERIFY( r4c(c) == 2 );
> +
> + // Incompatible signatures
> + std::function_ref<long(CountedArg) const noexcept> r5r(r1);
> + VERIFY( r5r(c) == 2 );
> + std::function_ref<long(CountedArg) const noexcept> r5m(m1);
> + VERIFY( r5r(c) == 2 );
> + std::function_ref<long(CountedArg) const noexcept> r5c(c1);
> + VERIFY( r5r(c) == 2 );
> +}
> +
> +void
> +test02()
> +{
> + // Constructing move_only_function and copyable_function from function_ref,
> + // have not chance to restore manager, so we store function_ref inside.
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::function_ref<int(CountedArg) const noexcept> r1(f);
> +
> + std::move_only_function<int(CountedArg) const noexcept> m1(r1);
> + VERIFY( m1(c) == 2 );
> +
> + std::copyable_function<int(CountedArg) const noexcept> c1(r1);
> + VERIFY( c1(c) == 2 );
> +}
> +
> +void
> +test03()
> +{
> + struct F
> + {
> + int operator()(CountedArg const& arg) noexcept
> + { return arg.counter; }
> +
> + int operator()(CountedArg const& arg) const noexcept
> + { return arg.counter + 1000; }
> + };
> +
> + F f;
> + std::function_ref<int(CountedArg) const> r1(f);
> + VERIFY( r1(c) == 1001 );
> +
> + // Call const overload as std::function_ref<int(CountedArg) const>
> + // inside std::function_ref<int(CountedArg)> would do.
> + std::function_ref<int(CountedArg)> r2(r1);
> + VERIFY( r2(c) == 1002 );
> + std::move_only_function<int(CountedArg)> m2(r1);
> + VERIFY( m2(c) == 1002 );
> +
> + // Call non-const overload as const-qualifed operator() for
> + // std::function_ref<int(CountedArg)> do.
> + std::function_ref<int(CountedArg)> r3(f);
> + VERIFY( r3(c) == 1 );
> + std::function_ref<int(CountedArg) const> r4(r3);
> + VERIFY( r4(c) == 2 );
> + std::move_only_function<int(CountedArg) const> m4(r3);
> + VERIFY( m4(c) == 2 );
> +}
> +
> +void
> +test04()
> +{
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::function_ref<int(CountedArg)> w1(f);
> + // function_ref stores function_ref due incompatibile signatures
> + std::function_ref<int(CountedArg const&)> w2(std::move(w1));
> + // copy is made when passing to int(CountedArg)
> + VERIFY( w2(c) == 1 );
> + // wrapped 3 times
> + std::function_ref<int(CountedArg)> w3(w2);
> + VERIFY( w3(c) == 2 );
> + // wrapped 4 times
> + std::function_ref<int(CountedArg const&)> w4(w3);
> + VERIFY( w4(c) == 2 );
> + // wrapped 5 times
> + std::function_ref<int(CountedArg)> w5(w4);
> + VERIFY( w5(c) == 3 );
> +}
> +
> +void
> +test05()
> +{
> + // No special interoperability with std::function
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::function<int(CountedArg)> f1(f);
> + std::function_ref<int(CountedArg) const> c1(std::move(f1));
> + VERIFY( c1(c) == 2 );
> +
> + std::function_ref<int(CountedArg) const> c2(f);
> + std::function<int(CountedArg)> f2(c2);
> + VERIFY( f2(c) == 2 );
> +}
> +
> +int main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> + test05();
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> new file mode 100644
> index 00000000000..2940b876954
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> @@ -0,0 +1,103 @@
> +// { dg-do compile { target c++26 } }
> +
> +#include <functional>
> +#include <type_traits>
> +
> +using std::is_same_v;
> +using std::nontype;
> +using std::nontype_t;
> +using std::function_ref;
> +
> +int i = 0;
> +
> +void f0();
> +void f0n() noexcept;
> +
> +static_assert( is_same_v<decltype(function_ref(f0)),
> + function_ref<void()>> );
> +static_assert( is_same_v<decltype(function_ref(f0n)),
> + function_ref<void() noexcept>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f0>)),
> + function_ref<void()>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f0n>)),
> + function_ref<void() noexcept>> );
> +
> +void f1(int);
> +void f1n(int) noexcept;
> +
> +static_assert( is_same_v<decltype(function_ref(f1)),
> + function_ref<void(int)>> );
> +static_assert( is_same_v<decltype(function_ref(f1n)),
> + function_ref<void(int) noexcept>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f1>)),
> + function_ref<void(int)>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f1n>)),
> + function_ref<void(int) noexcept>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f1>, i)),
> + function_ref<void()>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f1n>, i)),
> + function_ref<void() noexcept>> );
> +
> +void f2(int*, int);
> +void f2n(int*, int) noexcept;
> +
> +static_assert( is_same_v<decltype(function_ref(f2)),
> + function_ref<void(int*, int)>> );
> +static_assert( is_same_v<decltype(function_ref(f2n)),
> + function_ref<void(int*, int) noexcept>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f2>)),
> + function_ref<void(int*, int)>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f2n>)),
> + function_ref<void(int*, int) noexcept>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f2>, &i)),
> + function_ref<void(int)>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<f2n>, &i)),
> + function_ref<void(int) noexcept>> );
> +
> +struct S
> +{
> + int mem;
> + int f();
> + int fn() noexcept;
> +
> + int fc(int) const;
> + int fcn(int) const noexcept;
> +
> + int fl(int) &;
> + int fln(int) & noexcept;
> +
> + int fcl(float) const&;
> + int fcln(float) const& noexcept;
> +};
> +S s{};
> +const S cs{};
> +
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, s)),
> + function_ref<int&()>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, cs)),
> + function_ref<const int&()>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, &s)),
> + function_ref<int&()>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, &cs)),
> + function_ref<const int&()>> );
> +
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::f>, s)),
> + function_ref<int()>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fn>, &s)),
> + function_ref<int() noexcept>> );
> +
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fc>, &s)),
> + function_ref<int(int)>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fcn>, s)),
> + function_ref<int(int) noexcept>> );
> +
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fl>, &s)),
> + function_ref<int(int)>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fln>, s)),
> + function_ref<int(int) noexcept>> );
> +
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fcl>, s)),
> + function_ref<int(float)>> );
> +static_assert( is_same_v<decltype(function_ref(nontype<&S::fcln>, &s)),
> + function_ref<int(float) noexcept>> );
> +
> --
> 2.49.0
>
>
