[PATCH] libstdc++: Remove non_type and replace it with constant_wrapper in function_ref
Jonathan Wakely
jwakely.gcc@gmail.com
Wed Apr 8 10:04:32 GMT 2026
On Wed, 8 Apr 2026, 10:46 Tomasz Kamiński, <tkaminsk@redhat.com> wrote:
> From: Matthias Kretz <m.kretz@gsi.de>
>
> This implements P3948R1: constant_wrapper is the only tool needed
> for passing constant expressions via function arguments.
>
> This changes function_ref from nontype_t to constant_wrapper and
> implements the ambiguity check (static_asert in function_ref
> from constant_wrapper constructor).
>
> In addition to P3948R1 this also includes the (forgotten) deduction
> guide changes suggested in the draft PR [1].
>
> [1] https://github.com/cplusplus/draft/pull/8878
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/funcref_impl.h (function_ref::function_ref):
> Change nontype_t parameter to constant_wrapper, and adjust
> accordingly. Add static_assert detecting ambigous semantics.
> (function_refoperator=): Detect constant_wrapper rather than
> nontype_t.
>
Missing :: here
* include/bits/funcwrap.h (function_ref): Change
> * include/bits/utility.h (std::nontype_t, std::nontype)
> (std::__is_nontype_v): Remove.
> (_is_constant_wrapper_v): Define.
>
And _ here
The patch itself is fine, so OK with those two tweaks to the changelog.
* src/c++23/std.cc.in (std::nontype_t, std::nontype):
> Remove exports.
> * testsuite/20_util/function_ref/cw_cons_neg.cc: New tests
> for ambiguity check.
> * testsuite/20_util/function_ref/assign.cc: Replace nontype_t
> with constant_wrapper and nontype with std::cw.
> * testsuite/20_util/function_ref/call.cc: Likewise.
> * testsuite/20_util/function_ref/cons.cc: Likewise.
> * testsuite/20_util/function_ref/cons_neg.cc: Likewise.
> * testsuite/20_util/function_ref/deduction.cc: Likewise.
> * testsuite/20_util/function_ref/mutation.cc: Likewise.
>
> Co-authored-by: Tomasz Kamiński <tkaminsk@redhat.com>
> Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
> Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
> ---
> This is based on Matthias patch from formge:
>
> https://forge.sourceware.org/gcc/gcc-TEST/pulls/147/commits/cac7355bcbd7ea8b5e26f064922e8f4412a4da97
>
> I have applied small adjustment to names and parameter specification,
> to be more consistient with the standard. Outside of that I have reworked
> static_assert to reflect more closely what is in the standard, and added
> negative test (cw_const_neg.cc).
>
> Testing on x86_64-linux. All *function_ref* test already passed in
> all standard modes and with modules. OK for trunk when all test passes?
>
>
> libstdc++-v3/include/bits/funcref_impl.h | 36 ++++----
> libstdc++-v3/include/bits/funcwrap.h | 13 +--
> libstdc++-v3/include/bits/utility.h | 23 ++---
> libstdc++-v3/src/c++23/std.cc.in | 4 -
> .../testsuite/20_util/function_ref/assign.cc | 27 +++---
> .../testsuite/20_util/function_ref/call.cc | 51 ++++++------
> .../testsuite/20_util/function_ref/cons.cc | 83 +++++++++----------
> .../20_util/function_ref/cons_neg.cc | 17 ++--
> .../20_util/function_ref/cw_cons_neg.cc | 35 ++++++++
> .../20_util/function_ref/dangling.cc | 2 +-
> .../20_util/function_ref/deduction.cc | 48 +++++------
> .../20_util/function_ref/mutation.cc | 9 +-
> 12 files changed, 185 insertions(+), 163 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/20_util/function_ref/cw_cons_neg.cc
>
> diff --git a/libstdc++-v3/include/bits/funcref_impl.h
> b/libstdc++-v3/include/bits/funcref_impl.h
> index 3d55c8406b0..9fcab570803 100644
> --- a/libstdc++-v3/include/bits/funcref_impl.h
> +++ b/libstdc++-v3/include/bits/funcref_impl.h
> @@ -129,12 +129,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> // _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)&>
> + template<auto __cwfn, typename _Fn>
> + requires __is_invocable_using<const _Fn&>
> constexpr
> - function_ref(nontype_t<__fn>) noexcept
> + function_ref(constant_wrapper<__cwfn, _Fn>) noexcept
> {
> - using _Fn = remove_cv_t<decltype(__fn)>;
> + constexpr const _Fn& __fn = constant_wrapper<__cwfn, _Fn>::value;
> + if constexpr (sizeof...(_ArgTypes) > 0)
> + if constexpr ((... &&
> _ConstExprParam<remove_cvref_t<_ArgTypes>>))
> + static_assert(!requires {
> + typename constant_wrapper<
> + std::__invoke(__fn,
> remove_cvref_t<_ArgTypes>::value...)>;
> + }, "cw<fn>(args...) should be equivalent to fn(args...)");
> +
> if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>)
> static_assert(__fn != nullptr);
>
> @@ -144,13 +151,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> /// 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>>
> + template<auto __cwfn, typename _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&>
> + && __is_invocable_using<const _Fn&, _Td _GLIBCXX_MOF_CV&>
> constexpr
> - function_ref(nontype_t<__fn>, _Up&& __ref) noexcept
> + function_ref(constant_wrapper<__cwfn, _Fn>, _Up&& __ref) noexcept
> {
> - using _Fn = remove_cv_t<decltype(__fn)>;
> + constexpr const _Fn& __fn = constant_wrapper<__cwfn, _Fn>::value;
> if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>)
> static_assert(__fn != nullptr);
>
> @@ -166,12 +174,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
> /// 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*>
> + template< auto __cwfn, typename _Fn, typename _Td>
> + requires __is_invocable_using<const _Fn&, _Td _GLIBCXX_MOF_CV*>
> constexpr
> - function_ref(nontype_t<__fn>, _Td _GLIBCXX_MOF_CV* __ptr) noexcept
> + function_ref(constant_wrapper<__cwfn, _Fn>, _Td _GLIBCXX_MOF_CV*
> __ptr) noexcept
> {
> - using _Fn = remove_cv_t<decltype(__fn)>;
> + constexpr const _Fn& __fn = constant_wrapper<__cwfn, _Fn>::value;
> if constexpr (is_pointer_v<_Fn> || is_member_pointer_v<_Fn>)
> static_assert(__fn != nullptr);
> if constexpr (is_member_pointer_v<_Fn>)
> @@ -182,8 +190,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> }
>
> template<typename _Tp>
> - requires (!is_same_v<_Tp, function_ref>)
> - && (!is_pointer_v<_Tp>) && (!__is_nontype_v<_Tp>)
> + requires (!is_same_v<_Tp, function_ref>) && (!is_pointer_v<_Tp>)
> + && (!__is_constant_wrapper_v<_Tp>)
> function_ref&
> operator=(_Tp) = delete;
>
> diff --git a/libstdc++-v3/include/bits/funcwrap.h
> b/libstdc++-v3/include/bits/funcwrap.h
> index 6441893d213..b835e075295 100644
> --- a/libstdc++-v3/include/bits/funcwrap.h
> +++ b/libstdc++-v3/include/bits/funcwrap.h
> @@ -573,15 +573,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> 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 __cwfn, typename _Fn>
> + requires is_function_v<remove_pointer_t<_Fn>>
> + function_ref(constant_wrapper<__cwfn, _Fn>)
> + -> function_ref<remove_pointer_t<_Fn>>;
>
> - template<auto __f, typename _Tp,
> + template<auto __cwfn, typename _Fn, typename _Tp,
> typename _SignaturePtr =
> - decltype(__polyfunc::__deduce_funcref<decltype(__f), _Tp&>())>
> + decltype(__polyfunc::__deduce_funcref<_Fn, _Tp&>())>
> requires (!is_void_v<_SignaturePtr>)
> - function_ref(nontype_t<__f>, _Tp&&)
> + function_ref(constant_wrapper<__cwfn, _Fn>, _Tp&&)
> -> function_ref<remove_pointer_t<_SignaturePtr>>;
>
> #endif // __glibcxx_function_ref
> diff --git a/libstdc++-v3/include/bits/utility.h
> b/libstdc++-v3/include/bits/utility.h
> index 970e63e8170..93e9e9f9dba 100644
> --- a/libstdc++-v3/include/bits/utility.h
> +++ b/libstdc++-v3/include/bits/utility.h
> @@ -458,6 +458,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { return value; }
> };
>
> + template<typename>
> + constexpr bool __is_constant_wrapper_v = false;
> +
> + template<auto __cw, typename _Fn>
> + constexpr bool __is_constant_wrapper_v<constant_wrapper<__cw, _Fn>> =
> true;
> +
> template<_CwFixedValue _Tp>
> constexpr auto cw = constant_wrapper<_Tp>{};
> #endif
> @@ -637,23 +643,6 @@ _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/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/
> std.cc.in
> index db66677d55b..3ac19871692 100644
> --- a/libstdc++-v3/src/c++23/std.cc.in
> +++ b/libstdc++-v3/src/c++23/std.cc.in
> @@ -3651,10 +3651,6 @@ 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
> index 9b02dc49c2a..521a35fc11e 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/assign.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/assign.cc
> @@ -8,8 +8,7 @@
> # error "Feature-test macro for function_ref has wrong value in
> <functional>"
> #endif
>
> -using std::nontype;
> -using std::nontype_t;
> +using std::constant_wrapper;
> using std::function_ref;
>
> using std::is_nothrow_move_assignable_v;
> @@ -55,13 +54,13 @@ 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>> );
> + constant_wrapper<funS>> );
> static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> - nontype_t<&funS>> );
> + constant_wrapper<&funS>> );
> static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> - nontype_t<&S::x>> );
> + constant_wrapper<&S::x>> );
> static_assert( is_nothrow_assignable_v<function_ref<int(S)>,
> - nontype_t<&S::f>> );
> + constant_wrapper<&S::f>> );
> struct Q
> {
> void operator()() const;
> @@ -75,22 +74,22 @@ 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{}>> );
> + constant_wrapper<Q{}>> );
> static_assert( is_nothrow_assignable_v<function_ref<void() const>,
> - nontype_t<Q{}>> );
> + constant_wrapper<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>;
> + function_ref<void(S)> fp(std::cw<funS>);
> + fp = std::cw<funS>;
> + fp = std::cw<&funS>;
> + fp = std::cw<&S::x>;
> + fp = std::cw<&S::f>;
>
> constexpr Q cq;
> function_ref<void() const> fq(cq);
> - fq = nontype<cq>;
> + fq = std::cw<cq>;
> return true;
> }
> static_assert( test_constexpr() );
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> index 49c6030b221..386c8de790a 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/call.cc
> @@ -4,7 +4,6 @@
> #include <utility>
> #include <testsuite_hooks.h>
>
> -using std::nontype;
> using std::function_ref;
>
> using std::is_same_v;
> @@ -43,7 +42,7 @@ test01()
> VERIFY( f0() == 0 );
> VERIFY( std::move(f0)() == 0 );
>
> - function_ref<int()> f1{nontype<F{}>};
> + function_ref<int()> f1{std::cw<F{}>};
> VERIFY( f1() == 1 );
> VERIFY( std::move(f1)() == 1 );
>
> @@ -53,7 +52,7 @@ test01()
> VERIFY( std::move(f2)() == 1 );
> VERIFY( std::move(std::as_const(f2))() == 1 );
>
> - function_ref<int() const> f3{nontype<F{}>};
> + function_ref<int() const> f3{std::cw<F{}>};
> VERIFY( f3() == 1 );
> VERIFY( std::as_const(f3)() == 1 );
> VERIFY( std::move(f3)() == 1 );
> @@ -71,11 +70,11 @@ test02()
> };
> F::Arg arg;
>
> - function_ref<int()> f0{std::nontype<F{}>, arg};
> + function_ref<int()> f0{std::cw<F{}>, arg};
> VERIFY( f0() == 0 );
> VERIFY( std::move(f0)() == 0 );
>
> - function_ref<int() const> f1{std::nontype<F{}>, arg};
> + function_ref<int() const> f1{std::cw<F{}>, arg};
> VERIFY( f1() == 1 );
> VERIFY( std::as_const(f1)() == 1 );
> }
> @@ -91,11 +90,11 @@ test03()
> };
> F::Arg arg;
>
> - function_ref<int()> f0{std::nontype<F{}>, &arg};
> + function_ref<int()> f0{std::cw<F{}>, &arg};
> VERIFY( f0() == 0 );
> VERIFY( std::move(f0)() == 0 );
>
> - function_ref<int() const> f1{std::nontype<F{}>, &arg};
> + function_ref<int() const> f1{std::cw<F{}>, &arg};
> VERIFY( f1() == 1 );
> VERIFY( std::as_const(f1)() == 1 );
> }
> @@ -108,7 +107,7 @@ test04()
> VERIFY( f0() == 0 );
> VERIFY( std::move(f0)() == 0 );
>
> - function_ref<int()> f1{nontype<fp>};
> + function_ref<int()> f1{std::cw<fp>};
> VERIFY( f1() == 0 );
> VERIFY( std::move(f1)() == 0 );
>
> @@ -116,7 +115,7 @@ test04()
> VERIFY( f2() == 0 );
> VERIFY( std::move(f2)() == 0 );
>
> - const function_ref<int() const> f3{nontype<fp>};
> + const function_ref<int() const> f3{std::cw<fp>};
> VERIFY( f2() == 0 );
> VERIFY( std::move(f2)() == 0 );
> }
> @@ -130,14 +129,14 @@ int callback_ref(ftype& f, int x) { return f(x); }
> void
> test05()
> {
> - function_ref<int(int)> r1(nontype<&callback_ptr>, &twice);
> + function_ref<int(int)> r1(std::cw<&callback_ptr>, &twice);
> VERIFY( r1(2) == 4 );
> - function_ref<int(int)> r2(nontype<&callback_ptr>, cube);
> + function_ref<int(int)> r2(std::cw<&callback_ptr>, cube);
> VERIFY( r2(2) == 8 );
>
> - function_ref<int(int)> r3(nontype<&callback_ref>, twice);
> + function_ref<int(int)> r3(std::cw<&callback_ref>, twice);
> VERIFY( r3(3) == 6 );
> - function_ref<int(int)> r4(nontype<&callback_ref>, cube);
> + function_ref<int(int)> r4(std::cw<&callback_ref>, cube);
> VERIFY( r4(3) == 27 );
> }
>
> @@ -174,37 +173,37 @@ test06()
> std::function_ref<const int&(int, int) const> e8(std::as_const(csr));
> VERIFY( &e8(0, 0) == &s.v );
>
> - std::function_ref<int&()> f1(std::nontype<&S::v>, sr);
> + std::function_ref<int&()> f1(std::cw<&S::v>, sr);
> VERIFY( &f1() == &s.v );
> - std::function_ref<const int&()> f2(std::nontype<&S::v>, sr);
> + std::function_ref<const int&()> f2(std::cw<&S::v>, sr);
> VERIFY( &f2() == &s.v );
> - std::function_ref<int&()> f3(std::nontype<&S::m>, sr);
> + std::function_ref<int&()> f3(std::cw<&S::m>, sr);
> VERIFY( &f3() == &s.v );
> - std::function_ref<const int&()> f4(std::nontype<&S::c>, sr);
> + std::function_ref<const int&()> f4(std::cw<&S::c>, sr);
> VERIFY( &f4() == &s.v );
>
> - std::function_ref<const int&()> f5(std::nontype<&S::v>, csr);
> + std::function_ref<const int&()> f5(std::cw<&S::v>, csr);
> VERIFY( &f5() == &s.v );
> - std::function_ref<const int&()> f6(std::nontype<&S::c>, sr);
> + std::function_ref<const int&()> f6(std::cw<&S::c>, sr);
> VERIFY( &f6() == &s.v );
> static_assert( !std::is_constructible_v<
> std::function_ref<int&()>,
> - std::nontype_t<&S::c>, std::reference_wrapper<S>&>
> + std::constant_wrapper<&S::c>, std::reference_wrapper<S>&>
> );
>
> - std::function_ref<int&()> f7(std::nontype<&S::v>, std::as_const(sr));
> + std::function_ref<int&()> f7(std::cw<&S::v>, std::as_const(sr));
> VERIFY( &f7() == &s.v );
> - std::function_ref<const int&()> f8(std::nontype<&S::m>,
> std::as_const(sr));
> + std::function_ref<const int&()> f8(std::cw<&S::m>, std::as_const(sr));
> VERIFY( &f8() == &s.v );
>
> // No rvalue reference_wrapper support
> static_assert( !std::is_constructible_v<
> std::function_ref<int&()>,
> - std::nontype_t<&S::v>, std::reference_wrapper<S>>
> + std::constant_wrapper<&S::v>, std::reference_wrapper<S>>
> );
> static_assert( !std::is_constructible_v<
> std::function_ref<int&()>,
> - std::nontype_t<&S::v>, std::reference_wrapper<const S>>
> + std::constant_wrapper<&S::v>, std::reference_wrapper<const S>>
> );
>
> // reference to reference_wrapper are bound, so mutation are visible
> @@ -232,9 +231,9 @@ test06()
> { return &x; };
>
> // identity of reference_wrapper is preserved
> - std::function_ref<const std::reference_wrapper<S>*()>
> g1(std::nontype<id>, sr);
> + std::function_ref<const std::reference_wrapper<S>*()> g1(std::cw<id>,
> sr);
> VERIFY( g1() == &sr );
> - std::function_ref<const std::reference_wrapper<const S>*()>
> g2(std::nontype<id>, csr);
> + std::function_ref<const std::reference_wrapper<const S>*()>
> g2(std::cw<id>, csr);
> VERIFY( g2() == &csr );
> }
>
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> index a91f5ba3dab..78aebd38a07 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/cons.cc
> @@ -9,8 +9,7 @@
> # error "Feature-test macro for function_ref has wrong value in
> <functional>"
> #endif
>
> -using std::nontype;
> -using std::nontype_t;
> +using std::constant_wrapper;
> using std::function_ref;
>
> using std::is_default_constructible_v;
> @@ -60,31 +59,31 @@ 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>> );
> + constant_wrapper<funS>> );
> static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> - nontype_t<&funS>> );
> + constant_wrapper<&funS>> );
> static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> - nontype_t<&S::x>> );
> + constant_wrapper<&S::x>> );
> static_assert( is_nothrow_constructible_v<function_ref<int(S)>,
> - nontype_t<&S::f>> );
> + constant_wrapper<&S::f>> );
>
> static_assert( is_nothrow_constructible_v<function_ref<int()>,
> - nontype_t<funS>, S&> );
> + constant_wrapper<funS>, S&> );
> static_assert( is_nothrow_constructible_v<function_ref<int()>,
> - nontype_t<&funS>, S&> );
> + constant_wrapper<&funS>, S&> );
> static_assert( is_nothrow_constructible_v<function_ref<int()>,
> - nontype_t<&S::x>, S&> );
> + constant_wrapper<&S::x>, S&> );
> static_assert( is_nothrow_constructible_v<function_ref<int()>,
> - nontype_t<&S::f>, S&> );
> + constant_wrapper<&S::f>, S&> );
>
> static_assert( ! is_constructible_v<function_ref<int()>,
> - nontype_t<funS>, S*> );
> + constant_wrapper<funS>, S*> );
> static_assert( ! is_constructible_v<function_ref<int()>,
> - nontype_t<&funS>, S*> );
> + constant_wrapper<&funS>, S*> );
> static_assert( is_nothrow_constructible_v<function_ref<int()>,
> - nontype_t<&S::x>, S*> );
> + constant_wrapper<&S::x>, S*> );
> static_assert( is_nothrow_constructible_v<function_ref<int()>,
> - nontype_t<&S::f>, S*> );
> + constant_wrapper<&S::f>, S*> );
>
> struct M
> {
> @@ -98,9 +97,9 @@ 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{}>> );
> + constant_wrapper<M{}>> );
> static_assert( ! is_constructible_v<function_ref<void() const>,
> - nontype_t<M{}>> );
> + constant_wrapper<M{}>> );
> struct Q
> {
> void operator()(int) const;
> @@ -115,22 +114,22 @@ 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{}>> );
> + constant_wrapper<Q{}>> );
> static_assert( is_nothrow_constructible_v<function_ref<void(int) const>,
> - nontype_t<Q{}>> );
> + constant_wrapper<Q{}>> );
> static_assert( is_nothrow_constructible_v<function_ref<void()>,
> - nontype_t<Q{}>, int&> );
> + constant_wrapper<Q{}>, int&> );
> static_assert( is_nothrow_constructible_v<function_ref<void() const>,
> - nontype_t<Q{}>, int&> );
> + constant_wrapper<Q{}>, int&> );
> static_assert( ! is_constructible_v<function_ref<void()>,
> - nontype_t<Q{}>, int> );
> + constant_wrapper<Q{}>, int> );
> static_assert( ! is_constructible_v<function_ref<void() const>,
> - nontype_t<Q{}>, int> );
> + constant_wrapper<Q{}>, int> );
>
> static_assert( is_nothrow_constructible_v<function_ref<void()>,
> - nontype_t<Q{}>, int*> );
> + constant_wrapper<Q{}>, int*> );
> static_assert( ! is_constructible_v<function_ref<void() const>,
> - nontype_t<Q{}>, int*> );
> + constant_wrapper<Q{}>, int*> );
>
> struct L
> {
> @@ -143,9 +142,9 @@ 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{}>> );
> + constant_wrapper<L{}>> );
> static_assert( ! is_constructible_v<function_ref<void() const>,
> - nontype_t<L{}>> );
> + constant_wrapper<L{}>> );
>
> struct R
> {
> @@ -159,24 +158,24 @@ 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{}>> );
> + constant_wrapper<R{}>> );
> static_assert( ! is_constructible_v<function_ref<void(float) const>,
> - nontype_t<R{}>> );
> + constant_wrapper<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>);
> + function_ref<void(S)> fp1(std::cw<funS>);
> + function_ref<void(S)> fp3(std::cw<&funS>);
> + function_ref<void(S)> fp4(std::cw<&S::x>);
> + function_ref<void(S)> fp5(std::cw<&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);
> + function_ref<void()> fp6(std::cw<&funS>, s);
> + function_ref<void()> fp7(std::cw<&S::x>, s);
> + function_ref<void()> fp8(std::cw<&S::x>, &s);
> + function_ref<void()> fp9(std::cw<&S::f>, s);
> + function_ref<void()> fp10(std::cw<&S::f>, &s);
>
> M m;
> function_ref<void()> fm1(m);
> @@ -190,13 +189,13 @@ test_constexpr()
>
> 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>);
> + function_ref<void(int)> fcq3(std::cw<cq>);
> + function_ref<void(int) const> fcq4(std::cw<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);
> + function_ref<void()> fcq5(std::cw<cq>, i);
> + function_ref<void() const> fcq6(std::cw<cq>, i);
> + function_ref<void()> fcq7(std::cw<cq>, &i);
>
> L l;
> function_ref<void()> fl1(l);
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> index 050090df370..a426ac64cd5 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/cons_neg.cc
> @@ -2,7 +2,6 @@
>
> #include <functional>
>
> -using std::nontype;
> using std::function_ref;
>
> struct S
> @@ -16,15 +15,15 @@ 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(S)> fd1(std::cw<fp>); // { dg-error "from here" }
> +function_ref<int(S)> fd2(std::cw<mdp>); // { dg-error "from here" }
> +function_ref<int(S)> fd3(std::cw<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()> br4(std::cw<fp>, s); // { dg-error "from here" }
> +function_ref<int()> br5(std::cw<mdp>, s); // { dg-error "from here" }
> +function_ref<int()> br6(std::cw<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" }
> +function_ref<int()> bp7(std::cw<mdp>, &s); // { dg-error "from here" }
> +function_ref<int()> bp8(std::cw<mfp>, &s); // { dg-error "from here" }
>
> // { dg-prune-output "static assertion failed" }
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/cw_cons_neg.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/cw_cons_neg.cc
> new file mode 100644
> index 00000000000..a295bc2ce31
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/cw_cons_neg.cc
> @@ -0,0 +1,35 @@
> +// { dg-do compile { target c++26 } }
> +
> +#include <functional>
> +
> +using std::function_ref;
> +using std::constant_wrapper;
> +
> +struct S
> +{
> + int operator()() const { return 1; }
> +
> + // Non-constant, so cw<S{}>(cw<1>) call never unwrapps
> + int operator()(int) const { return 1; }
> + template<auto __cw>
> + int operator()(constant_wrapper<__cw, int>) const { return 1; }
> +
> + // Constant, cw<S{}>(cw<1>, cw<2>) calls int overload
> + // while S{}(cw<1>, cw<1>) calls constant_wrapper overload
> + constexpr int operator()(int, int) const { return 1; }
> + template<auto __cw1, auto __cw2>
> + constexpr int operator()(constant_wrapper<__cw1, int>,
> + constant_wrapper<__cw2, int>)
> + { return 1; }
> +};
> +
> +function_ref<int()> f0a(S{});
> +
> +function_ref<int(int)> f1a(S{});
> +function_ref<int(constant_wrapper<2>)> f1b(std::cw<S{}>);
> +
> +function_ref<int(int, int)> f2a(std::cw<S{}>); // OK, runtime
> +function_ref<int(constant_wrapper<1>, int)> f2b(std::cw<S{}>); // OK,
> still runtime
> +function_ref<int(constant_wrapper<2>, constant_wrapper<3>)>
> f2c(std::cw<S{}>); // { dg-error "from here" }
> +
> +// { dg-prune-output "static assertion failed" }
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/dangling.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/dangling.cc
> index 3cc782524f6..4ef5d067555 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/dangling.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/dangling.cc
> @@ -46,7 +46,7 @@ struct NonStatic {
> { return x + y + v; }
> };
>
> -constexpr auto vNonType = create(std::nontype<NonStatic{3}>);
> +constexpr auto vNonType = create(std::cw<NonStatic{3}>);
>
> struct StaticWins {
> static int
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> index b034c7af072..63c3f6ea7e3 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/deduction.cc
> @@ -4,15 +4,13 @@
> #include <type_traits>
>
> using std::is_same_v;
> -using std::nontype;
> -using std::nontype_t;
> using std::function_ref;
>
> int i = 0;
>
> template<auto f, class... Args>
> concept deductible = requires (Args&... args)
> - { std::function_ref(std::nontype<f>, args...); };
> + { std::function_ref(std::cw<f>, args...); };
>
> static_assert( !deductible<1> );
> static_assert( !deductible<1, int> );
> @@ -24,9 +22,9 @@ 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>)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f0>)),
> function_ref<void()>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f0n>)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f0n>)),
> function_ref<void() noexcept>> );
> static_assert( !deductible<f0, char*> );
> static_assert( !deductible<f0n, char*> );
> @@ -38,13 +36,13 @@ 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>)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f1>)),
> function_ref<void(int)>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f1n>)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f1n>)),
> function_ref<void(int) noexcept>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f1>, i)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f1>, i)),
> function_ref<void()>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f1n>, i)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f1n>, i)),
> function_ref<void() noexcept>> );
> static_assert( !deductible<f1, char*> );
> static_assert( !deductible<f1n, char*> );
> @@ -56,13 +54,13 @@ 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>)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f2>)),
> function_ref<void(int*, int)>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f2n>)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f2n>)),
> function_ref<void(int*, int) noexcept>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f2>, &i)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f2>, &i)),
> function_ref<void(int)>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<f2n>, &i)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<f2n>, &i)),
> function_ref<void(int) noexcept>> );
> static_assert( !deductible<f2, char*> );
> static_assert( !deductible<f2n, char*> );
> @@ -88,40 +86,40 @@ struct S
> S s{};
> const S cs{};
>
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::mem>, s)),
> function_ref<int&() noexcept>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, cs)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::mem>, cs)),
> function_ref<const int&() noexcept>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, &s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::mem>, &s)),
> function_ref<int&() noexcept>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::mem>, &cs)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::mem>, &cs)),
> function_ref<const int&() noexcept>> );
> static_assert( !deductible<&S::mem, int> );
>
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::f>, s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::f>, s)),
> function_ref<int()>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fn>, &s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fn>, &s)),
> function_ref<int() noexcept>> );
> static_assert( !deductible<&S::f, char*> );
> static_assert( !deductible<&S::fn, char*> );
> static_assert( !deductible<&S::f, const S> );
> static_assert( !deductible<&S::fn, const S> );
>
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fc>, &s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fc>, &s)),
> function_ref<int(int)>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fcn>, s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fcn>, s)),
> function_ref<int(int) noexcept>> );
> static_assert( !deductible<&S::fc, char*> );
> static_assert( !deductible<&S::fcn, char*> );
>
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fl>, &s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fl>, &s)),
> function_ref<int(int)>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fln>, s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fln>, s)),
> function_ref<int(int) noexcept>> );
>
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fcl>, s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fcl>, s)),
> function_ref<int(float)>> );
> -static_assert( is_same_v<decltype(function_ref(nontype<&S::fcln>, &s)),
> +static_assert( is_same_v<decltype(function_ref(std::cw<&S::fcln>, &s)),
> function_ref<int(float) noexcept>> );
>
> static_assert( !deductible<&S::fr, char*> );
> diff --git a/libstdc++-v3/testsuite/20_util/function_ref/mutation.cc
> b/libstdc++-v3/testsuite/20_util/function_ref/mutation.cc
> index 32c6931e9a8..d55f4facbda 100644
> --- a/libstdc++-v3/testsuite/20_util/function_ref/mutation.cc
> +++ b/libstdc++-v3/testsuite/20_util/function_ref/mutation.cc
> @@ -3,7 +3,6 @@
> #include <functional>
> #include <testsuite_hooks.h>
>
> -using std::nontype;
> using std::function_ref;
>
> void
> @@ -55,8 +54,8 @@ test02()
> };
> S s{10};
>
> - function_ref<int()> r1(nontype<&S::x>, s);
> - function_ref<long()> r2(nontype<&S::x>, &s);
> + function_ref<int()> r1(std::cw<&S::x>, s);
> + function_ref<long()> r2(std::cw<&S::x>, &s);
>
> VERIFY( r1() == 10 );
> VERIFY( r2() == 10 );
> @@ -66,8 +65,8 @@ test02()
> VERIFY( r1() == 20 );
> VERIFY( r2() == 20 );
>
> - r1 = function_ref<int()>(nontype<&S::f>, &s);
> - r2 = function_ref<long()>(nontype<&S::f>, s);
> + r1 = function_ref<int()>(std::cw<&S::f>, &s);
> + r2 = function_ref<long()>(std::cw<&S::f>, s);
>
> VERIFY( r1() == 20 );
> VERIFY( r2() == 20 );
> --
> 2.53.0
>
>
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