On Mon, May 12, 2025 at 12:57 PM Tomasz Kamiński <tkami...@redhat.com>
wrote:
> Based on the provision in C++26 [func.wrap.general] p2 this patch adjust
> the generic
> move_only_function(_Fn&&) constructor, such that when _Fn refers to
> selected
> move_only_function instantiations, the ownership of the target object is
> direclty
> transfered to constructor object. This avoid cost of double indireciton in
> this situation.
> We apply this also in C++23 mode.
>
> We also fix handling of self assigments, to match behavior required by
> standard,
> due use of copy and swap idiom.
>
> An instantiations MF1 of move_only_function can transfer target of another
> instantiation MF2, if it can be constructed via usual rules
> (__is_callable_from<_MF2>),
> and their invoker are convertible (__is_invocer_convertible<MF2, MF1>()),
> i.e.:
> * MF1 is less noexcept than MF2,
> * return types are the same after stripping cv-quals
> * adujsted parameters type are the same (__poly::_param_t), i.e. param of
> types T and T&&
> are compatible for non-trivially copyable objects.
> Compatiblity of cv ref qualification is checked via
> __is_callable_from<_MF2>.
>
> To achieve above the generation of _M_invoke functions is moved to _Invoke
> class
> templates, that only depends on noexcept, return type and adjusted
> parameter of the
> signature. To make the invoker signature compatible between const and
> mutable
> qualified signatures, we always accept _Storage as const& and perform a
> const_cast
> for locally stored object. This approach guarantees that we never strip
> const from
> const object.
>
> Another benefit of this approach is that
> move_only_function<void(std::string)>
> and move_only_function<void(std::string&&)> use same funciton pointer,
> which should
> reduce binary size.
>
> The _Storage and _Manager functionality was also extracted and adjusted
> from
> _Mo_func base, in preparation for implementation for copyable_function and
> function_ref. The _Storage was adjusted to store functions pointers as
> void(*)().
> The manage function, now accepts _Op enum parameter, and supports
> additional
> operations:
> * _Op::_Address stores address of target object in destination
> * _Op::_Copy, when enabled, copies from source to destination
> Furthremore, we provide a type-independent mamange functions for handling
> all:
> * function pointer types
> * trivially copyable object stored locally.
> Similary as in case of invoker, we always pass source as const (for copy),
> and cast away constness in case of move operations, where we know that
> source
> is mutable.
>
> Finally, the new helpers are defined in __polyfunc internal namespace.
>
> PR libstdc++/119125
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/mofunc_impl.h: Added __glibcxx_move_only_function
> guard.
> (std::move_only_function): Adjusted for changes in
> bits/move_only_function.h
> (move_only_function::move_only_function(_Fn&&)): Special case
> move_only_functions
> with same invoker.
> (move_only_function::operator=(move_only_function&&)): Handle self
> assigment.
> * include/bits/move_only_function.h (__polyfunc::_Ptrs)
> (__polyfunc::_Storage): Refactored from _Mo_func::_Storage.
> (__polyfunc::_Manager): Refactored from _Mo_func::_S_manager.
> (__polyfunc::__param_t): Moved from move_only_function::__param_t.
> (__polyfunc::_Base_invoker, __polyfunc::_Invoke): Refactored from
> move_only_function::_S_invoke.
> (std::_Mofunc_base): Moved into __polyfunc::_Mo_base with parts
> extracted to __polyfunc::_Storage and __polyfunc::_Manager.
> (__polyfunc::__deref_as, __polyfunc::__invoker_of,
> __polyfunc::__base_of)
> (__polyfunc::__is_invoker_convertible): Define.
> (std::__is_move_only_function_v): Renamed to
> __is_polymorphic_function_v.
> (std::__is_polymorphic_function_v): Renamed from
> __is_polymorphic_function_v.
> * testsuite/20_util/move_only_function/conv.cc: New test.
> * testsuite/20_util/move_only_function/move.cc: Tests for self
> assigment.
> ---
> libstdc++-v3/include/bits/mofunc_impl.h | 75 +--
> .../include/bits/move_only_function.h | 449 +++++++++++++-----
> .../20_util/move_only_function/conv.cc | 188 ++++++++
> .../20_util/move_only_function/move.cc | 11 +
> 4 files changed, 569 insertions(+), 154 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/20_util/move_only_function/conv.cc
>
> diff --git a/libstdc++-v3/include/bits/mofunc_impl.h
> b/libstdc++-v3/include/bits/mofunc_impl.h
> index 318a55e618f..839f19e0389 100644
> --- a/libstdc++-v3/include/bits/mofunc_impl.h
> +++ b/libstdc++-v3/include/bits/mofunc_impl.h
> @@ -62,8 +62,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _Res, typename... _ArgTypes, bool _Noex>
> class move_only_function<_Res(_ArgTypes...) _GLIBCXX_MOF_CV
> _GLIBCXX_MOF_REF noexcept(_Noex)>
> - : _Mofunc_base
> + : __polyfunc::_Mo_base
> {
> + using _Base = __polyfunc::_Mo_base;
> + using _Invoker = __polyfunc::_Invoker<_Noex, _Res, _ArgTypes...>;
> + using _Signature = _Invoker::_Signature;
> +
> template<typename _Tp>
> using __callable
> = __conditional_t<_Noex,
> @@ -87,7 +91,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> /// Moves the target object, leaving the source empty.
> move_only_function(move_only_function&& __x) noexcept
> - : _Mofunc_base(static_cast<_Mofunc_base&&>(__x)),
> + : _Base(static_cast<_Base&&>(__x)),
> _M_invoke(std::__exchange(__x._M_invoke, nullptr))
> { }
>
> @@ -99,13 +103,26 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> {
> if constexpr (is_function_v<remove_pointer_t<_Vt>>
> || is_member_pointer_v<_Vt>
> - || __is_move_only_function_v<_Vt>)
> + || __is_polymorphic_function_v<_Vt>)
> {
> if (__f == nullptr)
> return;
> }
> - _M_init<_Vt>(std::forward<_Fn>(__f));
> - _M_invoke = &_S_invoke<_Vt>;
> + if constexpr (__is_polymorphic_function_v<_Vt>
> + && __polyfunc::__is_invoker_convertible<_Vt,
> move_only_function>())
> + {
> + // Handle cases where _Fn is const reference to
> copyable_function,
> + // by firstly creatiogn temporary and moving from it. This
> may move
> + // locally stored object twice.
> + _Vt __tmp(std::forward<_Fn>(__f));
> + _M_move(__polyfunc::__base_of(__tmp));
> + _M_invoke = std::__exchange(__polyfunc::__invoker_of(__tmp),
> nullptr);
> + }
> + else
> + {
> + _M_init<_Vt>(std::forward<_Fn>(__f));
> + _M_invoke = _Invoker::template _S_storage<_Vt
> _GLIBCXX_MOF_INV_QUALS>();
> + }
> }
>
> /// Stores a target object initialized from the arguments.
> @@ -115,7 +132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> explicit
> move_only_function(in_place_type_t<_Tp>, _Args&&... __args)
> noexcept(_S_nothrow_init<_Tp, _Args...>())
> - : _M_invoke(&_S_invoke<_Tp>)
> + : _M_invoke(_Invoker::template _S_storage<_Tp
> _GLIBCXX_MOF_INV_QUALS>())
> {
> static_assert(is_same_v<decay_t<_Tp>, _Tp>);
> _M_init<_Tp>(std::forward<_Args>(__args)...);
> @@ -129,7 +146,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> move_only_function(in_place_type_t<_Tp>, initializer_list<_Up>
> __il,
> _Args&&... __args)
> noexcept(_S_nothrow_init<_Tp, initializer_list<_Up>&, _Args...>())
> - : _M_invoke(&_S_invoke<_Tp>)
> + : _M_invoke(_Invoker::template _S_storage<_Tp
> _GLIBCXX_MOF_INV_QUALS>())
> {
> static_assert(is_same_v<decay_t<_Tp>, _Tp>);
> _M_init<_Tp>(__il, std::forward<_Args>(__args)...);
> @@ -139,8 +156,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> move_only_function&
> operator=(move_only_function&& __x) noexcept
> {
> - _Mofunc_base::operator=(static_cast<_Mofunc_base&&>(__x));
> - _M_invoke = std::__exchange(__x._M_invoke, nullptr);
> + // Standard requires support of self assigment, by specifying it as
> + // copy and swap.
> + if (this != addressof(__x)) [[likely]]
> + {
> + _Base::operator=(static_cast<_Base&&>(__x));
> + _M_invoke = std::__exchange(__x._M_invoke, nullptr);
> + }
> return *this;
> }
>
> @@ -148,7 +170,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> move_only_function&
> operator=(nullptr_t) noexcept
> {
> - _Mofunc_base::operator=(nullptr);
> + _M_reset();
> _M_invoke = nullptr;
> return *this;
> }
> @@ -167,7 +189,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> ~move_only_function() = default;
>
> /// True if a target object is present, false otherwise.
> - explicit operator bool() const noexcept { return _M_invoke !=
> nullptr; }
> + explicit operator bool() const noexcept
> + { return _M_invoke != nullptr; }
>
> /** Invoke the target object.
> *
> @@ -181,14 +204,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> operator()(_ArgTypes... __args) _GLIBCXX_MOF_CV_REF noexcept(_Noex)
> {
> __glibcxx_assert(*this != nullptr);
> - return _M_invoke(this, std::forward<_ArgTypes>(__args)...);
> + return _M_invoke(this->_M_storage,
> std::forward<_ArgTypes>(__args)...);
> }
>
> /// Exchange the target objects (if any).
> void
> swap(move_only_function& __x) noexcept
> {
> - _Mofunc_base::swap(__x);
> + _Base::swap(__x);
> std::swap(_M_invoke, __x._M_invoke);
> }
>
> @@ -203,25 +226,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { return __x._M_invoke == nullptr; }
>
> private:
> - template<typename _Tp>
> - using __param_t = __conditional_t<is_scalar_v<_Tp>, _Tp, _Tp&&>;
> + typename _Invoker::__storage_func_t _M_invoke = nullptr;
>
> - using _Invoker = _Res (*)(_Mofunc_base _GLIBCXX_MOF_CV*,
> - __param_t<_ArgTypes>...) noexcept(_Noex);
> + template<typename _Func>
> + friend auto&
> + __polyfunc::__invoker_of(_Func&) noexcept;
>
> - template<typename _Tp>
> - static _Res
> - _S_invoke(_Mofunc_base _GLIBCXX_MOF_CV* __self,
> - __param_t<_ArgTypes>... __args) noexcept(_Noex)
> - {
> - using _TpCv = _Tp _GLIBCXX_MOF_CV;
> - using _TpInv = _Tp _GLIBCXX_MOF_INV_QUALS;
> - return std::__invoke_r<_Res>(
> - std::forward<_TpInv>(*_S_access<_TpCv>(__self)),
> - std::forward<__param_t<_ArgTypes>>(__args)...);
> - }
> + template<typename _Func>
> + friend auto&
> + __polyfunc::__base_of(_Func&) noexcept;
>
> - _Invoker _M_invoke = nullptr;
> + template<typename _Dst, typename _Src>
> + friend consteval bool
> + __polyfunc::__is_invoker_convertible() noexcept;
> };
>
> #undef _GLIBCXX_MOF_CV_REF
> diff --git a/libstdc++-v3/include/bits/move_only_function.h
> b/libstdc++-v3/include/bits/move_only_function.h
> index 42b33d01901..58d6f2ee29e 100644
> --- a/libstdc++-v3/include/bits/move_only_function.h
> +++ b/libstdc++-v3/include/bits/move_only_function.h
> @@ -45,145 +45,343 @@ namespace std _GLIBCXX_VISIBILITY(default)
> {
> _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> - template<typename... _Signature>
> - class move_only_function; // not defined
> -
> /// @cond undocumented
> - class _Mofunc_base
> - {
> - protected:
> - _Mofunc_base() noexcept
> - : _M_manage(_S_empty)
> - { }
> -
> - _Mofunc_base(_Mofunc_base&& __x) noexcept
> - {
> - _M_manage = std::__exchange(__x._M_manage, _S_empty);
> - _M_manage(_M_storage, &__x._M_storage);
> - }
> -
> - template<typename _Tp, typename... _Args>
> - static constexpr bool
> - _S_nothrow_init() noexcept
> - {
> - if constexpr (__stored_locally<_Tp>)
> - return is_nothrow_constructible_v<_Tp, _Args...>;
> - return false;
> - }
> -
> - template<typename _Tp, typename... _Args>
> - void
> - _M_init(_Args&&... __args) noexcept(_S_nothrow_init<_Tp,
> _Args...>())
> - {
> - if constexpr (__stored_locally<_Tp>)
> - ::new (_M_storage._M_addr()) _Tp(std::forward<_Args>(__args)...);
> - else
> - _M_storage._M_p = new _Tp(std::forward<_Args>(__args)...);
> -
> - _M_manage = &_S_manage<_Tp>;
> - }
> -
> - _Mofunc_base&
> - operator=(_Mofunc_base&& __x) noexcept
> - {
> - _M_manage(_M_storage, nullptr);
> - _M_manage = std::__exchange(__x._M_manage, _S_empty);
> - _M_manage(_M_storage, &__x._M_storage);
> - return *this;
> - }
> -
> - _Mofunc_base&
> - operator=(nullptr_t) noexcept
> - {
> - _M_manage(_M_storage, nullptr);
> - _M_manage = _S_empty;
> - return *this;
> - }
> -
> - ~_Mofunc_base() { _M_manage(_M_storage, nullptr); }
> -
> - void
> - swap(_Mofunc_base& __x) noexcept
> - {
> - // Order of operations here is more efficient if __x is empty.
> - _Storage __s;
> - __x._M_manage(__s, &__x._M_storage);
> - _M_manage(__x._M_storage, &_M_storage);
> - __x._M_manage(_M_storage, &__s);
> - std::swap(_M_manage, __x._M_manage);
> - }
> -
> - template<typename _Tp, typename _Self>
> - static _Tp*
> - _S_access(_Self* __self) noexcept
> - {
> - if constexpr (__stored_locally<remove_const_t<_Tp>>)
> - return static_cast<_Tp*>(__self->_M_storage._M_addr());
> - else
> - return static_cast<_Tp*>(__self->_M_storage._M_p);
> - }
> + template<typename _Tp>
> + constexpr bool __is_polymorphic_function_v = false;
>
> - private:
> - struct _Storage
> + namespace __polyfunc
> + {
> + union _Ptrs
> {
> - void* _M_addr() noexcept { return &_M_bytes[0]; }
> - const void* _M_addr() const noexcept { return &_M_bytes[0]; }
> -
> - // We want to have enough space to store a simple delegate type.
> - struct _Delegate { void (_Storage::*__pfm)(); _Storage* __obj; };
> - union {
> - void* _M_p;
> - alignas(_Delegate) alignas(void(*)())
> - unsigned char _M_bytes[sizeof(_Delegate)];
> - };
> + void* _M_obj;
> + void (*_M_func)();
> };
>
> - template<typename _Tp>
> - static constexpr bool __stored_locally
> - = sizeof(_Tp) <= sizeof(_Storage) && alignof(_Tp) <=
> alignof(_Storage)
> - && is_nothrow_move_constructible_v<_Tp>;
> -
> - // A function that either destroys the target object stored in
> __target,
> - // or moves the target object from *__src to __target.
> - using _Manager = void (*)(_Storage& __target, _Storage* __src)
> noexcept;
> + struct _Storage
> + {
> + void* _M_addr() noexcept { return &_M_bytes[0]; }
> + void const* _M_addr() const noexcept { return &_M_bytes[0]; }
> +
> + template<typename _Tp>
> + static consteval bool
> + _S_stored_locally() noexcept
> + {
> + return sizeof(_Tp) <= sizeof(_Storage)
> + && alignof(_Tp) <= alignof(_Storage)
> + && is_nothrow_move_constructible_v<_Tp>;
> + }
> +
> + template<typename _Tp, typename... _Args>
> + static consteval bool
> + _S_nothrow_init() noexcept
> + {
> + if constexpr (_S_stored_locally<_Tp>())
> + return is_nothrow_constructible_v<_Tp, _Args...>;
> + return false;
> + }
> +
> + template<typename _Tp, typename... _Args>
> + void
> + _M_init(_Args&&... __args) noexcept(_S_nothrow_init<_Tp,
> _Args...>())
> + {
> + if constexpr (is_function_v<remove_pointer_t<_Tp>>)
> + {
> + static_assert( sizeof...(__args) <= 1 );
> + // __args can have up to one element, returns nullptr if
> empty.
> + _Tp __func = (nullptr, ..., __args);
> + _M_ptrs._M_func = reinterpret_cast<void(*)>(__func);
> + }
> + else if constexpr (!_S_stored_locally<_Tp>())
> + _M_ptrs._M_obj = new _Tp(std::forward<_Args>(__args)...);
> + else
> + ::new (_M_addr()) _Tp(std::forward<_Args>(__args)...);
> + }
> +
> + template<typename _Tp>
> + _Tp* _M_ptr() const noexcept
> + {
> + if constexpr (is_function_v<remove_cv_t<_Tp>>)
> + return reinterpret_cast<_Tp*>(_M_ptrs._M_func);
> + else 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>
> + _Ref _M_ref() const noexcept
> + {
> + using _Tp = remove_reference_t<_Ref>;
> + return static_cast<_Ref>(*_M_ptr<_Tp>());
>
This will try to read function pointer from _M_obj, instead of _M_func.
I need to add test for this.
> + }
> +
> + // We want to have enough space to store a simple delegate type.
> + struct _Delegate { void (_Storage::*__pfm)(); _Storage* __obj; };
> + union {
> + _Ptrs _M_ptrs;
> + alignas(_Delegate) alignas(void(*)())
> + unsigned char _M_bytes[sizeof(_Delegate)];
> + };
> + };
> +
> + struct _Manager
> + {
> + enum class _Op
> + {
> + // saves address of entity in *__src to __target._M_ptrs,
> + _Address,
> + // moves entity stored in *__src to __target, __src becomes empty
> + _Move,
> + // copies entity stored in *__src to __target, supported only if
> + // _ProvideCopy is specified.
> + _Copy,
> + // destroys entity stored in __target, __src is ignoring
> + _Destroy,
> + };
> +
> + // A function that performs operation __op on the __target and
> possibly __src.
> + using _Func = void (*)(_Op __op, _Storage& __target, const _Storage*
> __src) noexcept;
>
> // The no-op manager function for objects with no target.
> - static void _S_empty(_Storage&, _Storage*) noexcept { }
> + static void _S_empty(_Op, _Storage&, const _Storage*) noexcept { }
>
> - // The real manager function for a target object of type _Tp.
> - template<typename _Tp>
> - static void
> - _S_manage(_Storage& __target, _Storage* __src) noexcept
> + template<bool _ProvideCopy, typename _Tp>
> + consteval static auto
> + _S_select()
> {
> - if constexpr (__stored_locally<_Tp>)
> - {
> - if (__src)
> - {
> - _Tp* __rval = static_cast<_Tp*>(__src->_M_addr());
> - ::new (__target._M_addr()) _Tp(std::move(*__rval));
> - __rval->~_Tp();
> - }
> - else
> - static_cast<_Tp*>(__target._M_addr())->~_Tp();
> - }
> + if constexpr (is_function_v<remove_pointer_t<_Tp>>)
> + return &_S_func;
> + else if constexpr (!_Storage::_S_stored_locally<_Tp>())
> + return &_S_ptr<_ProvideCopy, _Tp>;
> + else if constexpr (is_trivially_copyable_v<_Tp>)
> + return &_S_trivial;
> else
> - {
> - if (__src)
> - __target._M_p = __src->_M_p;
> - else
> - delete static_cast<_Tp*>(__target._M_p);
> - }
> + return &_S_local<_ProvideCopy, _Tp>;
> }
>
> - _Storage _M_storage;
> - _Manager _M_manage;
> - };
> + private:
> + static void
> + _S_func(_Op __op, _Storage& __target, const _Storage* __src) noexcept
> + {
> + switch (__op)
> + {
> + case _Op::_Address:
> + case _Op::_Move:
> + case _Op::_Copy:
> + __target._M_ptrs._M_func = __src->_M_ptrs._M_func;
> + return;
> + case _Op::_Destroy:
> + return;
> + }
> + }
> +
> + static void
> + _S_trivial(_Op __op, _Storage& __target, const _Storage* __src)
> noexcept
> + {
> + switch (__op)
> + {
> + case _Op::_Address:
> + __target._M_ptrs._M_obj = const_cast<void*>(__src->_M_addr());
> + return;
> + case _Op::_Move:
> + case _Op::_Copy:
> + // N.B. _Storage starts lifetime of _M_bytes char array,
> + // that implicitly creates, amongst other, are possibly
> trivially
> + // copyable objects, so we copy any present in __src.
> + new (&__target) _Storage(*__src);
> + return;
> + case _Op::_Destroy:
> + return;
> + }
> + }
> +
> + template<bool _Provide_copy, typename _Tp>
> + static void
> + _S_local(_Op __op, _Storage& __target, const _Storage* __src)
> + noexcept(!_Provide_copy)
> + {
> + switch (__op)
> + {
> + case _Op::_Address:
> + __target._M_ptrs._M_obj = __src->_M_ptr<_Tp>();
> + return;
> + case _Op::_Move:
> + {
> + _Tp* __obj = __src->_M_ptr<_Tp>();
> + ::new(__target._M_addr()) _Tp(std::move(*__obj));
> + __obj->~_Tp();
> + }
> + return;
> + case _Op::_Destroy:
> + __target._M_ptr<_Tp>()->~_Tp();
> + return;
> + case _Op::_Copy:
> + if constexpr (_Provide_copy)
> + ::new (__target._M_addr()) _Tp(__src->_M_ref<const _Tp&>());
> + else
> + __builtin_unreachable();
> + return;
> + }
> + }
> +
> + template<bool _Provide_copy, typename _Tp>
> + static void
> + _S_ptr(_Op __op, _Storage& __target, const _Storage* __src)
> + noexcept(!_Provide_copy)
> + {
> + switch (__op)
> + {
> + case _Op::_Address:
> + case _Op::_Move:
> + __target._M_ptrs._M_obj = __src->_M_ptrs._M_obj;
> + return;
> + case _Op::_Destroy:
> + ::delete __target._M_ptr<_Tp>();
> + return;
> + case _Op::_Copy:
> + if constexpr (_Provide_copy)
> + __target._M_ptrs._M_obj = ::new _Tp(__src->_M_ref<const
> _Tp&>());
> + else
> + __builtin_unreachable();
> + return;
> + }
> + }
> + };
> +
> + template<bool _Noex, typename _Ret, typename... _Args>
> + struct _Base_invoker
> + {
> + using _Signature = _Ret(*)(_Args...) noexcept(_Noex);
> +
> + using __storage_func_t = _Ret(*)(const _Storage&, _Args...)
> noexcept(_Noex);
> + template<typename _Tp>
> + static consteval __storage_func_t
> + _S_storage()
> + { return &_S_call_storage<_Adjust_target<_Tp>>; }
> +
> + private:
> + template<typename _Tp, typename _Td = remove_cvref_t<_Tp>>
> + using _Adjust_target =
> + __conditional_t<is_pointer_v<_Td> || is_member_pointer_v<_Td>,
> _Td, _Tp>;
> +
> + template<typename _Tp>
> + static _Ret
> + _S_call_storage(const _Storage& __ref, _Args... __args)
> noexcept(_Noex)
> + {
> + // N.B. static_cast<_Args> in contrast to forward<_Args> does
> not bind
> + // reference if argument is passed by value.
> + return std::__invoke_r<_Ret>(__ref._M_ref<_Tp>(),
> + static_cast<_Args>(__args)...);
> + }
> + };
> +
> + template<typename _Tp>
> + using __param_t = __conditional_t<is_scalar_v<_Tp>, _Tp, _Tp&&>;
> +
> + template<bool _Noex, typename _Ret, typename... _Args>
> + using _Invoker = _Base_invoker<_Noex, remove_cv_t<_Ret>,
> __param_t<_Args>...>;
> +
> + class _Mo_base
> + {
> + protected:
> + _Mo_base() noexcept
> + : _M_manage(_Manager::_S_empty)
> + { }
> +
> + _Mo_base(_Mo_base&& __x) noexcept
> + { _M_move(__x); }
> +
> + template<typename _Tp, typename... _Args>
> + static consteval bool
> + _S_nothrow_init() noexcept
> + { return _Storage::_S_nothrow_init<_Tp, _Args...>(); }
> +
> + template<typename _Tp, typename... _Args>
> + void
> + _M_init(_Args&&... __args)
> + noexcept(_S_nothrow_init<_Tp, _Args...>())
> + {
> + _M_storage._M_init<_Tp>(std::forward<_Args>(__args)...);
> + _M_manage = _Manager::_S_select<false, _Tp>();
> + }
> +
> + void _M_move(_Mo_base& __x) noexcept
> + {
> + using _Op = _Manager::_Op;
> + _M_manage = std::__exchange(__x._M_manage, _Manager::_S_empty);
> + _M_manage(_Op::_Move, _M_storage, &__x._M_storage);
> + }
> +
> + _Mo_base&
> + operator=(_Mo_base&& __x) noexcept
> + {
> + _M_destroy();
> + _M_move(__x);
> + return *this;
> + }
> +
> + void _M_reset() noexcept
> + {
> + _M_destroy();
> + _M_manage = _Manager::_S_empty;
> + }
> +
> + ~_Mo_base()
> + { _M_destroy(); }
> +
> + void
> + swap(_Mo_base& __x) noexcept
> + {
> + using _Op = _Manager::_Op;
> + // Order of operations here is more efficient if __x is empty.
> + _Storage __s;
> + __x._M_manage(_Op::_Move, __s, &__x._M_storage);
> + _M_manage(_Op::_Move, __x._M_storage, &_M_storage);
> + __x._M_manage(_Op::_Move, _M_storage, &__s);
> + std::swap(_M_manage, __x._M_manage);
> + }
> +
> + _Storage _M_storage;
> +
> + private:
> + void _M_destroy() noexcept
> + { _M_manage(_Manager::_Op::_Destroy, _M_storage, nullptr); }
> +
> + _Manager::_Func _M_manage;
> + };
> +
> + template<typename _Func>
> + auto&
> + __invoker_of(_Func& __f) noexcept
> + { return __f._M_invoke; }
> +
> + template<typename _Func>
> + auto&
> + __base_of(_Func& __f) noexcept
> + { return static_cast<__like_t<_Func&, typename _Func::_Base>>(__f); }
> +
> + template<typename _Src, typename _Dst>
> + consteval bool
> + __is_invoker_convertible() noexcept
> + {
> + if constexpr (requires { typename _Src::_Signature; })
> + return is_convertible_v<typename _Src::_Signature,
> + typename _Dst::_Signature>;
> + else
> + return false;
> + }
> +} // namespace __polyfunc
> + /// @endcond
>
> + template<typename... _Signature>
> + class move_only_function; // not defined
> +
> + /// @cond undocumented
> template<typename _Tp>
> - inline constexpr bool __is_move_only_function_v = false;
> - template<typename _Tp>
> - constexpr bool __is_move_only_function_v<move_only_function<_Tp>> =
> true;
> - /// @endcond
> + constexpr bool __is_polymorphic_function_v<move_only_function<_Tp>> =
> true;
>
> namespace __detail::__variant
> {
> @@ -196,6 +394,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> : true_type
> { };
> } // namespace __detail::__variant
> + /// @endcond
>
> _GLIBCXX_END_NAMESPACE_VERSION
> } // namespace std
> diff --git a/libstdc++-v3/testsuite/20_util/move_only_function/conv.cc
> b/libstdc++-v3/testsuite/20_util/move_only_function/conv.cc
> new file mode 100644
> index 00000000000..3da5e9e90a3
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/move_only_function/conv.cc
> @@ -0,0 +1,188 @@
> +// { dg-do run { target c++23 } }
> +// { dg-require-effective-target hosted }
> +
> +#include <functional>
> +#include <testsuite_hooks.h>
> +
> +using std::move_only_function;
> +
> +static_assert( !std::is_constructible_v<std::move_only_function<void()>,
> + std::move_only_function<void()&>>
> );
> +static_assert( !std::is_constructible_v<std::move_only_function<void()>,
> + std::move_only_function<void()&&>>
> );
> +static_assert( !std::is_constructible_v<std::move_only_function<void()&>,
> + std::move_only_function<void()&&>>
> );
> +static_assert( !std::is_constructible_v<std::move_only_function<void()
> const>,
> + std::move_only_function<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;
> +
> +// When move_only_functions is constructed from other move_only_function,
> +// the compiler can avoid double indirection per C++26
> [func.wrap.general] p2.
> +
> +void
> +test01()
> +{
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::move_only_function<int(CountedArg) const noexcept> m1(f);
> + VERIFY( m1(c) == 1 );
> +
> + std::move_only_function<int(CountedArg) const> m2(std::move(m1));
> + VERIFY( m2(c) == 1 );
> +
> + std::move_only_function<int(CountedArg)> m3(std::move(m2));
> + VERIFY( m3(c) == 1 );
> +
> + // Invokers internally uses Counted&& for non-trivial types,
> + // sinature remain compatible.
> + std::move_only_function<int(CountedArg&&)> m4(std::move(m3));
> + VERIFY( m4({}) == 0 );
> +
> + std::move_only_function<int(CountedArg&&)&&> m5(std::move(m4));
> + VERIFY( std::move(m5)({}) == 0 );
> +
> + m4 = f;
> + std::move_only_function<int(CountedArg&&)&> m7(std::move(m4));
> + VERIFY( m7({}) == 0 );
> +
> + m4 = f;
> + std::move_only_function<int(CountedArg&&)&> m8(std::move(m4));
> + VERIFY( m8({}) == 0 );
> +
> + // Incompatible signatures
> + m1 = f;
> + std::move_only_function<long(CountedArg) const noexcept>
> m9(std::move(m1));
> + VERIFY( m9(c) == 2 );
> +}
> +
> +void
> +test02()
> +{
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::move_only_function<int(CountedArg) const noexcept> m1(f);
> + VERIFY( m1(c) == 1 );
> +
> + std::move_only_function<int(CountedArg) const> m2;
> + m2 = std::move(m1);
> + VERIFY( m2(c) == 1 );
> +
> + std::move_only_function<int(CountedArg)> m3;
> + m3 = std::move(m2);
> + VERIFY( m3(c) == 1 );
> +
> + // Invokers internally uses Counted&& for non-trivial types,
> + // sinature remain compatible.
> + std::move_only_function<int(CountedArg&&)> m4;
> + m4 = std::move(m3);
> + VERIFY( m4({}) == 0 );
> +
> + std::move_only_function<int(CountedArg&&)&&> m5;
> + m5 = std::move(m4);
> + VERIFY( std::move(m5)({}) == 0 );
> +
> + m4 = f;
> + std::move_only_function<int(CountedArg&&)&> m7;
> + m7 = std::move(m4);
> + VERIFY( m7({}) == 0 );
> +
> + m4 = f;
> + std::move_only_function<int(CountedArg&&)&> m8;
> + m8 = std::move(m4);
> + VERIFY( m8({}) == 0 );
> +
> + m1 = f;
> + std::move_only_function<long(CountedArg) const noexcept> m9;
> + m9 = std::move(m1);
> + VERIFY( m9(c) == 2 );
> +}
> +
> +void
> +test03()
> +{
> + std::move_only_function<int(long) const noexcept> e;
> + VERIFY( e == nullptr );
> +
> + std::move_only_function<int(long) const> e2(std::move(e));
> + VERIFY( e2 == nullptr );
> + e2 = std::move(e);
> + VERIFY( e2 == nullptr );
> +
> + std::move_only_function<bool(int) const> e3(std::move(e));
> + VERIFY( e3 == nullptr );
> + e3 = std::move(e);
> + VERIFY( e3 == nullptr );
> +}
> +
> +void
> +test04()
> +{
> + 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::move_only_function<int(CountedArg) const> m1(f);
> + VERIFY( m1(c) == 1001 );
> +
> + // Call const overload as std::move_only_function<int(CountedArg) const>
> + // inside std::move_only_function<int(CountedArg)> would do.
> + std::move_only_function<int(CountedArg)> m2(std::move(m1));
> + VERIFY( m2(c) == 1001 );
> +
> + std::move_only_function<int(CountedArg)> m3(f);
> + VERIFY( m3(c) == 1 );
> +}
> +
> +void
> +test05()
> +{
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::move_only_function<int(CountedArg)> w1(f);
> + // move_only_function stores move_only_function due incompatibile
> signatures
> + std::move_only_function<int(CountedArg const&)> w2(std::move(w1));
> + // copy is made when passing to int(CountedArg)
> + VERIFY( w2(c) == 1 );
> + // wrapped 3 times
> + w1 = std::move(w2);
> + VERIFY( w1(c) == 2 );
> + // wrapped 4 times
> + w2 = std::move(w1);
> + VERIFY( w2(c) == 2 );
> + // wrapped 5 times
> + w1 = std::move(w2);
> + VERIFY( w1(c) == 3 );
> +}
> +
> +void
> +test06()
> +{
> + // No special interoperability with std::function
> + auto f = [](CountedArg const& arg) noexcept { return arg.counter; };
> + std::function<int(CountedArg)> f1(f);
> + std::move_only_function<int(CountedArg) const> m1(std::move(f1));
> + VERIFY( m1(c) == 2 );
> +}
> +
> +int main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> + test05();
> + test06();
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/move_only_function/move.cc
> b/libstdc++-v3/testsuite/20_util/move_only_function/move.cc
> index 51e31a6323d..6da02c9cd81 100644
> --- a/libstdc++-v3/testsuite/20_util/move_only_function/move.cc
> +++ b/libstdc++-v3/testsuite/20_util/move_only_function/move.cc
> @@ -32,6 +32,12 @@ test01()
> VERIFY( m1().copy == 1 );
> VERIFY( m1().move == 0 );
>
> + // Standard specifies move assigment as copy and swap
> + m1 = std::move(m1);
> + VERIFY( m1 != nullptr );
> + VERIFY( m1().copy == 1 );
> + VERIFY( m1().move == 0 );
> +
> // This will move construct a new target object and destroy the old one:
> auto m2 = std::move(m1);
> VERIFY( m1 == nullptr && m2 != nullptr );
> @@ -80,6 +86,11 @@ test02()
> VERIFY( m1().copy == 1 );
> VERIFY( m1().move == 0 );
>
> + m1 = std::move(m1);
> + VERIFY( m1 != nullptr );
> + VERIFY( m1().copy == 1 );
> + VERIFY( m1().move == 0 );
> +
> // The target object is on the heap so this just moves a pointer:
> auto m2 = std::move(m1);
> VERIFY( m1 == nullptr && m2 != nullptr );
> --
> 2.49.0
>
>
