[PATCH v2] libstdc++: Refactor bound arguments storage for bind_front/back
Patrick Palka
ppalka@redhat.com
Tue Aug 26 13:53:49 GMT 2025
On Wed, 20 Aug 2025, Tomasz Kamiński wrote:
> This patch refactors the implementation of bind_front and bind_back to
> avoid using std::tuple for argument storage. Instead, bound arguments are
> now:
> * stored directly if there is only one,
> * within a dedicated _Bound_arg_storage otehrwise.
I think I forgot the motivation of this change. What's the benefit of
replacing std::tuple here? Does _Bound_arg_storage allow for more a
more compact memory layout?
>
> _Bound_arg_storage holds each argument in an _Indexed_bound_arg base object.
> The base class is parameterized by both type and index to allow storing
> multiple arguments of the same type. Invocations are handled by _S_apply_front
> amd _S_apply_back static functions, which simulate explicit object parameters.
> To facilitate this, the __like_t alias template is now unconditionally available
> since C++11 in bits/move.h.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/move.h (std::__like_impl, std::__like_t): Make
> available in c++11.
> * include/std/functional (std::_Indexed_bound_arg)
> (std::_Bound_arg_storage, std::__make_bound_args): Define.
> (std::_Bind_front, std::_Bind_back): Use _Bound_arg_storage.
> * testsuite/20_util/function_objects/bind_back/1.cc: Expand
> test to cover cases of 0, 1, many bound args.
> * testsuite/20_util/function_objects/bind_back/111327.cc: Likewise.
> * testsuite/20_util/function_objects/bind_front/1.cc: Likewise.
> * testsuite/20_util/function_objects/bind_front/111327.cc: Likewise.
>
> Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
> ---
> Changes in v2:
> * replace few 8 spaces with tabs
> * add more test cases, covering materialization
>
> Testing on x86_64-linux, all bind test passed.
> OK for trunk when test passes.
>
> libstdc++-v3/include/bits/move.h | 2 +-
> libstdc++-v3/include/std/functional | 113 +++++++++---
> .../20_util/function_objects/bind_back/1.cc | 166 ++++++++++++++++--
> .../function_objects/bind_back/111327.cc | 11 ++
> .../20_util/function_objects/bind_front/1.cc | 164 +++++++++++++++--
> .../function_objects/bind_front/111327.cc | 11 ++
> 6 files changed, 418 insertions(+), 49 deletions(-)
>
> diff --git a/libstdc++-v3/include/bits/move.h b/libstdc++-v3/include/bits/move.h
> index 061e6b4de3d..8c4f461a110 100644
> --- a/libstdc++-v3/include/bits/move.h
> +++ b/libstdc++-v3/include/bits/move.h
> @@ -89,7 +89,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> return static_cast<_Tp&&>(__t);
> }
>
> -#if __glibcxx_forward_like // C++ >= 23
> template<typename _Tp, typename _Up>
> struct __like_impl; // _Tp must be a reference and _Up an lvalue reference
>
> @@ -112,6 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> template<typename _Tp, typename _Up>
> using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
>
> +#if __glibcxx_forward_like // C++ >= 23
> /** @brief Forward with the cv-qualifiers and value category of another type.
> * @tparam _Tp An lvalue reference or rvalue reference.
> * @tparam _Up An lvalue reference type deduced from the function argument.
> diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
> index 307bcb95bcc..b1cda87929d 100644
> --- a/libstdc++-v3/include/std/functional
> +++ b/libstdc++-v3/include/std/functional
> @@ -922,6 +922,53 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> }
>
> #ifdef __cpp_lib_bind_front // C++ >= 20
> + template<size_t, typename _Tp>
> + struct _Indexed_bound_arg
> + {
> + [[no_unique_address]] _Tp _M_val;
> + };
> +
> + template<typename... _IndexedArgs>
> + struct _Bound_arg_storage : _IndexedArgs...
> + {
> + template<typename _Fd, typename _Self, typename... _CallArgs>
> + static constexpr
> + decltype(auto)
> + _S_apply_front(_Fd&& __fd, _Self&& __self, _CallArgs&&... __call_args)
> + {
> + return std::invoke(std::forward<_Fd>(__fd),
> + __like_t<_Self, _IndexedArgs>(__self)._M_val...,
> + std::forward<_CallArgs>(__call_args)...);
> + }
> +
> + template<typename _Fd, typename _Self, typename... _CallArgs>
> + static constexpr
> + decltype(auto)
> + _S_apply_back(_Fd&& __fd, _Self&& __self, _CallArgs&&... __call_args)
> + {
> + return std::invoke(std::forward<_Fd>(__fd),
> + std::forward<_CallArgs>(__call_args)...,
> + __like_t<_Self, _IndexedArgs>(__self)._M_val...);
> + }
> + };
> +
> + template<typename... _BoundArgs, typename... _Args>
> + constexpr auto
> + __make_bound_args(_Args&&... __args)
> + {
> + if constexpr (sizeof...(_BoundArgs) == 1)
> + // pack has one element, so return copy of arg
> + return (_BoundArgs(std::forward<_Args>(__args)), ...);
> + else
> + {
> + auto __impl = [&]<size_t... _Inds>(index_sequence<_Inds...>)
> + {
> + return _Bound_arg_storage<_Indexed_bound_arg<_Inds, _BoundArgs>...>
> + { {_BoundArgs(std::forward<_Args>(__args))}... };
> + };
> + return __impl(index_sequence_for<_BoundArgs...>());
> + }
> + }
>
> template<typename _Fd, typename... _BoundArgs>
> struct _Bind_front
> @@ -937,7 +984,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(__and_<is_nothrow_constructible<_Fd, _Fn>,
> is_nothrow_constructible<_BoundArgs, _Args>...>::value)
> : _M_fd(std::forward<_Fn>(__fn)),
> - _M_bound_args(std::forward<_Args>(__args)...)
> + _M_bound_args(__make_bound_args<_BoundArgs...>(std::forward<_Args>(__args)...))
> { static_assert(sizeof...(_Args) == sizeof...(_BoundArgs)); }
>
> #if __cpp_explicit_this_parameter
> @@ -948,7 +995,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_invocable_v<__like_t<_Self, _Fd>,
> __like_t<_Self, _BoundArgs>..., _CallArgs...>)
> {
> - return _S_call(__like_t<_Self, _Bind_front>(__self), _BoundIndices(),
> + return _S_call(__like_t<_Self, _Bind_front>(__self),
> std::forward<_CallArgs>(__call_args)...);
> }
> #else
> @@ -959,8 +1006,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> operator()(_CallArgs&&... __call_args) &
> noexcept(is_nothrow_invocable_v<_Fd&, _BoundArgs&..., _CallArgs...>)
> {
> - return _S_call(*this, _BoundIndices(),
> - std::forward<_CallArgs>(__call_args)...);
> + return _S_call(*this, std::forward<_CallArgs>(__call_args)...);
> }
>
> template<typename... _CallArgs>
> @@ -971,8 +1017,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_invocable_v<const _Fd&, const _BoundArgs&...,
> _CallArgs...>)
> {
> - return _S_call(*this, _BoundIndices(),
> - std::forward<_CallArgs>(__call_args)...);
> + return _S_call(*this, std::forward<_CallArgs>(__call_args)...);
> }
>
> template<typename... _CallArgs>
> @@ -982,8 +1027,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> operator()(_CallArgs&&... __call_args) &&
> noexcept(is_nothrow_invocable_v<_Fd, _BoundArgs..., _CallArgs...>)
> {
> - return _S_call(std::move(*this), _BoundIndices(),
> - std::forward<_CallArgs>(__call_args)...);
> + return _S_call(std::move(*this),
> + std::forward<_CallArgs>(__call_args)...);
> }
>
> template<typename... _CallArgs>
> @@ -994,8 +1039,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_invocable_v<const _Fd, const _BoundArgs...,
> _CallArgs...>)
> {
> - return _S_call(std::move(*this), _BoundIndices(),
> - std::forward<_CallArgs>(__call_args)...);
> + return _S_call(std::move(*this),
> + std::forward<_CallArgs>(__call_args)...);
> }
>
> template<typename... _CallArgs>
> @@ -1012,20 +1057,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> #endif
>
> private:
> - using _BoundIndices = index_sequence_for<_BoundArgs...>;
> + using _BoundArgsStorage
> + // _BoundArgs are required to be move-constructible, so this is valid.
> + = decltype(__make_bound_args<_BoundArgs...>(std::declval<_BoundArgs>()...));
>
> - template<typename _Tp, size_t... _Ind, typename... _CallArgs>
> + template<typename _Tp, typename... _CallArgs>
> static constexpr
> decltype(auto)
> - _S_call(_Tp&& __g, index_sequence<_Ind...>, _CallArgs&&... __call_args)
> + _S_call(_Tp&& __g, _CallArgs&&... __call_args)
> {
> - return std::invoke(std::forward<_Tp>(__g)._M_fd,
> - std::get<_Ind>(std::forward<_Tp>(__g)._M_bound_args)...,
> - std::forward<_CallArgs>(__call_args)...);
> + if constexpr (sizeof...(_BoundArgs) == 1)
> + return std::invoke(std::forward<_Tp>(__g)._M_fd,
> + std::forward<_Tp>(__g)._M_bound_args,
> + std::forward<_CallArgs>(__call_args)...);
> + else
> + return _BoundArgsStorage::_S_apply_front(
> + std::forward<_Tp>(__g)._M_fd,
> + std::forward<_Tp>(__g)._M_bound_args,
> + std::forward<_CallArgs>(__call_args)...);
> }
>
> [[no_unique_address]] _Fd _M_fd;
> - [[no_unique_address]] std::tuple<_BoundArgs...> _M_bound_args;
> + [[no_unique_address]] _BoundArgsStorage _M_bound_args;
> };
>
> template<typename _Fn, typename... _Args>
> @@ -1066,7 +1119,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(__and_<is_nothrow_constructible<_Fd, _Fn>,
> is_nothrow_constructible<_BoundArgs, _Args>...>::value)
> : _M_fd(std::forward<_Fn>(__fn)),
> - _M_bound_args(std::forward<_Args>(__args)...)
> + _M_bound_args(__make_bound_args<_BoundArgs...>(std::forward<_Args>(__args)...))
> { static_assert(sizeof...(_Args) == sizeof...(_BoundArgs)); }
>
> template<typename _Self, typename... _CallArgs>
> @@ -1076,25 +1129,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_invocable_v<__like_t<_Self, _Fd>,
> _CallArgs..., __like_t<_Self, _BoundArgs>...>)
> {
> - return _S_call(__like_t<_Self, _Bind_back>(__self), _BoundIndices(),
> + return _S_call(__like_t<_Self, _Bind_back>(__self),
> std::forward<_CallArgs>(__call_args)...);
> }
>
> private:
> - using _BoundIndices = index_sequence_for<_BoundArgs...>;
> + using _BoundArgsStorage
> + // _BoundArgs are required to be move-constructible, so this is valid.
> + = decltype(__make_bound_args<_BoundArgs...>(std::declval<_BoundArgs>()...));
>
> - template<typename _Tp, size_t... _Ind, typename... _CallArgs>
> + template<typename _Tp, typename... _CallArgs>
> static constexpr
> decltype(auto)
> - _S_call(_Tp&& __g, index_sequence<_Ind...>, _CallArgs&&... __call_args)
> + _S_call(_Tp&& __g, _CallArgs&&... __call_args)
> {
> - return std::invoke(std::forward<_Tp>(__g)._M_fd,
> - std::forward<_CallArgs>(__call_args)...,
> - std::get<_Ind>(std::forward<_Tp>(__g)._M_bound_args)...);
> + if constexpr (sizeof...(_BoundArgs) == 1)
> + return std::invoke(std::forward<_Tp>(__g)._M_fd,
> + std::forward<_CallArgs>(__call_args)...,
> + std::forward<_Tp>(__g)._M_bound_args);
> + else
> + return _BoundArgsStorage::_S_apply_back(
> + std::forward<_Tp>(__g)._M_fd,
> + std::forward<_Tp>(__g)._M_bound_args,
> + std::forward<_CallArgs>(__call_args)...);
> }
>
> [[no_unique_address]] _Fd _M_fd;
> - [[no_unique_address]] std::tuple<_BoundArgs...> _M_bound_args;
> + [[no_unique_address]] _BoundArgsStorage _M_bound_args;
> };
>
> template<typename _Fn, typename... _Args>
> diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_back/1.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_back/1.cc
> index c31d3228815..a31528fc755 100644
> --- a/libstdc++-v3/testsuite/20_util/function_objects/bind_back/1.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_back/1.cc
> @@ -48,6 +48,16 @@ test01()
> decltype(bind_back(std::declval<const F&>(), std::declval<const int&>()))
> >);
>
> + static_assert(std::is_same_v<
> + decltype(bind_back(std::declval<F>(), std::declval<int>(), std::declval<float>())),
> + decltype(bind_back(std::declval<F&>(), std::declval<int&>(), std::declval<float&>()))
> + >);
> + static_assert(std::is_same_v<
> + decltype(bind_back(std::declval<F>(), std::declval<int>(), std::declval<float>())),
> + decltype(bind_back(std::declval<const F&>(), std::declval<const int&>(), std::declval<const float&>()))
> + >);
> +
> +
> // Reference wrappers should be handled:
> static_assert(!std::is_same_v<
> decltype(bind_back(std::declval<F>(), std::declval<int&>())),
> @@ -63,29 +73,58 @@ test01()
> >);
> }
>
> +struct quals
> +{
> + bool as_const;
> + bool as_lvalue;
> +};
> +
> +template<typename... Args>
> void
> -test02()
> +testTarget(Args... args)
> {
> - struct quals
> + struct F
> {
> - bool as_const;
> - bool as_lvalue;
> + quals operator()(Args...) & { return { false, true }; }
> + quals operator()(Args...) const & { return { true, true }; }
> + quals operator()(Args...) && { return { false, false }; }
> + quals operator()(Args...) const && { return { true, false }; }
> };
>
> + F f;
> + auto g = bind_back(f, args...);
> + const auto& cg = g;
> + quals q;
> +
> + // constness and value category should be forwarded to the target object:
> + q = g();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = std::move(g)();
> + VERIFY( ! q.as_const && ! q.as_lvalue );
> + q = cg();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = std::move(cg)();
> + VERIFY( q.as_const && ! q.as_lvalue );
> +}
> +
> +template<typename... Args>
> +void
> +testBoundArgs(Args... args)
> +{
> struct F
> {
> - quals operator()() & { return { false, true }; }
> - quals operator()() const & { return { true, true }; }
> - quals operator()() && { return { false, false }; }
> - quals operator()() const && { return { true, false }; }
> + quals operator()(Args..., int&) const { return { false, true }; }
> + quals operator()(Args..., int const&) const { return { true, true }; }
> + quals operator()(Args..., int&&) const { return { false, false }; }
> + quals operator()(Args..., int const&&) const { return { true, false }; }
> };
>
> F f;
> - auto g = bind_back(f);
> + auto g = bind_back(f, args..., 10);
> const auto& cg = g;
> quals q;
>
> - // constness and value category should be forwarded to the target object:
> + // constness and value category should be forwarded to the bound objects:
> q = g();
> VERIFY( ! q.as_const && q.as_lvalue );
> q = std::move(g)();
> @@ -94,6 +133,70 @@ test02()
> VERIFY( q.as_const && q.as_lvalue );
> q = std::move(cg)();
> VERIFY( q.as_const && ! q.as_lvalue );
> +
> + int i = 0;
> + auto gr = bind_back(f, args..., std::ref(i));
> + const auto& cgr = gr;
> +
> + // bound object is reference wrapper
> + q = gr();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = std::move(gr)();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = cgr();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = std::move(cgr)();
> + VERIFY( ! q.as_const && q.as_lvalue );
> +
> + auto gcr = bind_back(f, args..., std::cref(i));
> + const auto& cgcr = gcr;
> +
> + q = gcr();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = std::move(gcr)();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = cgcr();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = std::move(cgcr)();
> + VERIFY( q.as_const && q.as_lvalue );
> +}
> +
> +template<typename... Args>
> +void
> +testCallArgs(Args... args)
> +{
> + struct F
> + {
> + quals operator()(int&, Args...) const { return { false, true }; }
> + quals operator()(int const&, Args...) const { return { true, true }; }
> + quals operator()(int&&, Args...) const { return { false, false }; }
> + quals operator()(int const&&, Args...) const { return { true, false }; }
> + };
> +
> + F f;
> + auto g = bind_back(f, args...);
> + const auto& cg = g;
> + quals q;
> + int i = 10;
> + const int ci = i;
> +
> + q = g(i);
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = g(std::move(i));
> + VERIFY( ! q.as_const && ! q.as_lvalue );
> + q = g(ci);
> + VERIFY( q.as_const && q.as_lvalue );
> + q = g(std::move(ci));
> + VERIFY( q.as_const && ! q.as_lvalue );
> +
> + q = cg(i);
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = cg(std::move(i));
> + VERIFY( ! q.as_const && ! q.as_lvalue );
> + q = cg(ci);
> + VERIFY( q.as_const && q.as_lvalue );
> + q = cg(std::move(ci));
> + VERIFY( q.as_const && ! q.as_lvalue );
> }
>
> void
> @@ -168,11 +271,52 @@ test04()
> return true;
> }
>
> +struct CountedArg
> +{
> + CountedArg() = default;
> + CountedArg(CountedArg&& f) noexcept : counter(f.counter) { ++counter; }
> + CountedArg& operator=(CountedArg&&) = delete;
> +
> + int counter = 0;
> +};
> +CountedArg const c;
> +
> +void
> +testMaterialization()
> +{
> + struct F
> + {
> + int operator()(CountedArg arg, int) const
> + { return arg.counter; };
> + };
> +
> + // CountedArg is bound to rvalue-reference thus moved
> + auto f0 = std::bind_back(F{});
> + VERIFY( f0(CountedArg(), 10) == 1 );
> +
> + auto f1 = std::bind_back(F{}, 10);
> + VERIFY( f1(CountedArg()) == 1 );
> +}
> +
> int
> main()
> {
> test01();
> - test02();
> test03();
> +
> + testTarget();
> + testTarget(10);
> + testTarget(10, 20, 30);
> +
> + testBoundArgs();
> + testBoundArgs(10);
> + testBoundArgs(10, 20, 30);
> +
> + testCallArgs();
> + testCallArgs(10);
> + testCallArgs(10, 20, 30);
> +
> + testMaterialization();
> +
> static_assert(test04());
> }
> diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_back/111327.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_back/111327.cc
> index d634db9dc1d..de3ae47e37f 100644
> --- a/libstdc++-v3/testsuite/20_util/function_objects/bind_back/111327.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_back/111327.cc
> @@ -37,6 +37,17 @@ int main() {
> g1(); // { dg-error "deleted|no match" }
> std::move(g1)(); // { dg-error "deleted|no match" }
> std::move(std::as_const(g1))();
> +
> + auto f2 = std::bind_back(F{}, 42, 10);
> + f2(); // { dg-error "deleted|no match" }
> + std::move(f2)();
> + std::as_const(f2)();
> + std::move(std::as_const(f2))();
> +
> + auto g2 = std::bind_back(G{}, 42, 10);
> + g2(); // { dg-error "deleted|no match" }
> + std::move(g2)(); // { dg-error "deleted|no match" }
> + std::move(std::as_const(g2))();
> }
>
> // { dg-error "no type named 'type' in 'struct std::invoke_result" "" { target c++23 } 0 }
> diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/1.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/1.cc
> index 57482c52263..ef28de8321b 100644
> --- a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/1.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/1.cc
> @@ -48,6 +48,15 @@ test01()
> decltype(bind_front(std::declval<const F&>(), std::declval<const int&>()))
> >);
>
> + static_assert(std::is_same_v<
> + decltype(bind_front(std::declval<F>(), std::declval<int>(), std::declval<float>())),
> + decltype(bind_front(std::declval<F&>(), std::declval<int&>(), std::declval<float&>()))
> + >);
> + static_assert(std::is_same_v<
> + decltype(bind_front(std::declval<F>(), std::declval<int>(), std::declval<float>())),
> + decltype(bind_front(std::declval<const F&>(), std::declval<const int&>(), std::declval<const float&>()))
> + >);
> +
> // Reference wrappers should be handled:
> static_assert(!std::is_same_v<
> decltype(bind_front(std::declval<F>(), std::declval<int&>())),
> @@ -63,29 +72,58 @@ test01()
> >);
> }
>
> +struct quals
> +{
> + bool as_const;
> + bool as_lvalue;
> +};
> +
> +template<typename... Args>
> void
> -test02()
> +testTarget(Args... args)
> {
> - struct quals
> + struct F
> {
> - bool as_const;
> - bool as_lvalue;
> + quals operator()(Args...) & { return { false, true }; }
> + quals operator()(Args...) const & { return { true, true }; }
> + quals operator()(Args...) && { return { false, false }; }
> + quals operator()(Args...) const && { return { true, false }; }
> };
>
> + F f;
> + auto g = bind_front(f, args...);
> + const auto& cg = g;
> + quals q;
> +
> + // constness and value category should be forwarded to the target object:
> + q = g();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = std::move(g)();
> + VERIFY( ! q.as_const && ! q.as_lvalue );
> + q = cg();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = std::move(cg)();
> + VERIFY( q.as_const && ! q.as_lvalue );
> +}
> +
> +template<typename... Args>
> +void
> +testBoundArgs(Args... args)
> +{
> struct F
> {
> - quals operator()() & { return { false, true }; }
> - quals operator()() const & { return { true, true }; }
> - quals operator()() && { return { false, false }; }
> - quals operator()() const && { return { true, false }; }
> + quals operator()(Args..., int&) const { return { false, true }; }
> + quals operator()(Args..., int const&) const { return { true, true }; }
> + quals operator()(Args..., int&&) const { return { false, false }; }
> + quals operator()(Args..., int const&&) const { return { true, false }; }
> };
>
> F f;
> - auto g = bind_front(f);
> + auto g = bind_front(f, args..., 10);
> const auto& cg = g;
> quals q;
>
> - // constness and value category should be forwarded to the target object:
> + // constness and value category should be forwarded to the bound objects:
> q = g();
> VERIFY( ! q.as_const && q.as_lvalue );
> q = std::move(g)();
> @@ -94,6 +132,70 @@ test02()
> VERIFY( q.as_const && q.as_lvalue );
> q = std::move(cg)();
> VERIFY( q.as_const && ! q.as_lvalue );
> +
> + int i = 0;
> + auto gr = bind_front(f, args..., std::ref(i));
> + const auto& cgr = gr;
> +
> + // bound object is reference wrapper, converts to same type of reference
> + q = gr();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = std::move(gr)();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = cgr();
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = std::move(cgr)();
> + VERIFY( ! q.as_const && q.as_lvalue );
> +
> + auto gcr = bind_front(f, args..., std::cref(i));
> + const auto& cgcr = gcr;
> +
> + q = gcr();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = std::move(gcr)();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = cgcr();
> + VERIFY( q.as_const && q.as_lvalue );
> + q = std::move(cgcr)();
> + VERIFY( q.as_const && q.as_lvalue );
> +}
> +
> +template<typename... Args>
> +void
> +testCallArgs(Args... args)
> +{
> + struct F
> + {
> + quals operator()(Args..., int&) const { return { false, true }; }
> + quals operator()(Args..., int const&) const { return { true, true }; }
> + quals operator()(Args..., int&&) const { return { false, false }; }
> + quals operator()(Args..., int const&&) const { return { true, false }; }
> + };
> +
> + F f;
> + auto g = bind_front(f, args...);
> + const auto& cg = g;
> + quals q;
> + int i = 10;
> + const int ci = i;
> +
> + q = g(i);
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = g(std::move(i));
> + VERIFY( ! q.as_const && ! q.as_lvalue );
> + q = g(ci);
> + VERIFY( q.as_const && q.as_lvalue );
> + q = g(std::move(ci));
> + VERIFY( q.as_const && ! q.as_lvalue );
> +
> + q = cg(i);
> + VERIFY( ! q.as_const && q.as_lvalue );
> + q = cg(std::move(i));
> + VERIFY( ! q.as_const && ! q.as_lvalue );
> + q = cg(ci);
> + VERIFY( q.as_const && q.as_lvalue );
> + q = cg(std::move(ci));
> + VERIFY( q.as_const && ! q.as_lvalue );
> }
>
> void
> @@ -167,11 +269,51 @@ test04()
> VERIFY( bind_front(g2, 3)() == 6 );
> }
>
> +struct CountedArg
> +{
> + CountedArg() = default;
> + CountedArg(CountedArg&& f) noexcept : counter(f.counter) { ++counter; }
> + CountedArg& operator=(CountedArg&&) = delete;
> +
> + int counter = 0;
> +};
> +CountedArg const c;
> +
> +void
> +testMaterialization()
> +{
> + struct F
> + {
> + int operator()(int, CountedArg arg) const
> + { return arg.counter; };
> + };
> +
> + // CountedArg is bound to rvalue-reference thus moved
> + auto f0 = std::bind_front(F{});
> + VERIFY( f0(10, CountedArg()) == 1 );
> +
> + auto f1 = std::bind_front(F{}, 10);
> + VERIFY( f1(CountedArg()) == 1 );
> +}
> +
> int
> main()
> {
> test01();
> - test02();
> test03();
> test04();
> +
> + testTarget();
> + testTarget(10);
> + testTarget(10, 20, 30);
> +
> + testBoundArgs();
> + testBoundArgs(10);
> + testBoundArgs(10, 20, 30);
> +
> + testCallArgs();
> + testCallArgs(10);
> + testCallArgs(10, 20, 30);
> +
> + testMaterialization();
> }
> diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
> index 5fe0a83baec..6694322d67e 100644
> --- a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
> @@ -37,6 +37,17 @@ int main() {
> g1(); // { dg-error "deleted|no match" }
> std::move(g1)(); // { dg-error "deleted|no match" }
> std::move(std::as_const(g1))();
> +
> + auto f2 = std::bind_front(F{}, 42, 10);
> + f2(); // { dg-error "deleted|no match" }
> + std::move(f2)();
> + std::as_const(f2)();
> + std::move(std::as_const(f2))();
> +
> + auto g2 = std::bind_front(G{}, 42, 10);
> + g2(); // { dg-error "deleted|no match" }
> + std::move(g2)(); // { dg-error "deleted|no match" }
> + std::move(std::as_const(g2))();
> }
>
> // { dg-error "no type named 'type' in 'struct std::invoke_result" "" { target c++23 } 0 }
> --
> 2.50.1
>
>
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