On Wed, 14 May 2025, Tomasz Kaminski wrote:
>
>
> On Wed, May 14, 2025 at 9:41 AM Tomasz Kaminski <tkami...@redhat.com> wrote:
>
>
> On Tue, May 13, 2025 at 11:16 PM Patrick Palka <ppa...@redhat.com> wrote:
> On Mon, 12 May 2025, Tomasz Kamiński 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/call.cc: Test for
> functions pointers.
> > * 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 | 454
> +++++++++++++-----
> > .../20_util/move_only_function/call.cc | 14 +
> > .../20_util/move_only_function/conv.cc | 188 ++++++++
> > .../20_util/move_only_function/move.cc | 11 +
> > 5 files changed, 588 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
>
> typo, 'creating'
>
> > + // 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&
>
> Should be indented two spaces more than template-head
>
> > + __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;
>
> Spaces/tab issue on this line
>
> >
> > - _Invoker _M_invoke = nullptr;
> > + template<typename _Dst, typename _Src>
> > + friend consteval bool
>
> Should be a tab instead of spaces
>
> > + __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..5eb688a0ef4 100644
> > --- a/libstdc++-v3/include/bits/move_only_function.h
> > +++ b/libstdc++-v3/include/bits/move_only_function.h
> > @@ -45,145 +45,348 @@ 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)...);
>
> Why is global operator new/delete used in some call sites but not
> others?
>
> It should always be global new, fixing it.
>
> I have checked, and previously we were using a global placement, when using
> storage,
> that was paired with explicit invocaiton of destructor. However, for heap
> allocating new
> we were using non-global new and matching delete. I think I will preserve
> that, there is
> no reason to non-use user provided new when allocating on heap.
>
>
> > - 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;
>
> This should be 'inline' I think, otherwise there might be 'std' module
> issues?
>
> Isn't them being a variable template sufficient?
> I have added inline, because __is_move_only_function was inline.
Oops, I mistakenly thought GCC doesn't yet implement CWG2387, but we do
for GCC 15 since r15-2798-g82cd63a63eaa61, so the 'inline' indeed is
unnecessary. Sorry about that!
>
> >
> > - 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>
> > + [[__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 {
> > + _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
>
> Missing newline before function name
>
> > + {
> > + 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
>
> Same
>
> LGTM otherwise
>
> > + {
> > + _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 +399,7 @@ _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/call.cc
> b/libstdc++-v3/testsuite/20_util/move_only_function/call.cc
> > index bfc609afe37..217de374763 100644
> > --- a/libstdc++-v3/testsuite/20_util/move_only_function/call.cc
> > +++ b/libstdc++-v3/testsuite/20_util/move_only_function/call.cc
> > @@ -190,6 +190,19 @@ test04()
> > VERIFY( std::move(std::as_const(f5))() == 3 );
> > }
> >
> > +void
> > +test05()
> > +{
> > + int (*fp)() = [] { return 0; };
> > + move_only_function<int()> f0{fp};
> > + VERIFY( f0() == 0 );
> > + VERIFY( std::move(f0)() == 0 );
> > +
> > + const move_only_function<int() const> f1{fp};
> > + VERIFY( f1() == 0 );
> > + VERIFY( std::move(f1)() == 0 );
> > +}
> > +
> > struct Incomplete;
> >
> > void
> > @@ -206,5 +219,6 @@ int main()
> > test02();
> > test03();
> > test04();
> > + test05();
> > test_params();
> > }
> > 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
> >
> >
>
>
>
