[libcxx-commits] [libcxx] [libc++][functional] Implement `std::bind_front<NTTP>` (PR #165096)

[via libcxx-commits]

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@@ -49,6 +51,53 @@ _LIBCPP_HIDE_FROM_ABI constexpr auto bind_front(_Fn&& __f, _Args&&... __args) {
 
 #endif // _LIBCPP_STD_VER >= 20
 
+#if _LIBCPP_STD_VER >= 26
+
+template <auto _Fn, class _Indices, class... _BoundArgs>
+struct __nttp_bind_front_t;
+
+template <auto _Fn, size_t... _Indices, class... _BoundArgs>
+struct __nttp_bind_front_t<_Fn, index_sequence<_Indices...>, _BoundArgs...> {
+  tuple<_BoundArgs...> __bound_args_;
+
+  template <class _Self, class... _Args>
+  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(this _Self&& __self, _Args&&... __args) noexcept(noexcept(std::invoke(
+      _Fn, std::get<_Indices>(std::forward<_Self>(__self).__bound_args_)..., std::forward<_Args>(__args)...)))
+      -> decltype(std::invoke(
+          _Fn, std::get<_Indices>(std::forward<_Self>(__self).__bound_args_)..., std::forward<_Args>(__args)...)) {
+    return std::invoke(
+        _Fn, std::get<_Indices>(std::forward<_Self>(__self).__bound_args_)..., std::forward<_Args>(__args)...);
+  }
+};
+
+template <auto _Fn>
+struct __nttp_bind_without_bound_args_t {
+  template <class... _Args>
+  _LIBCPP_HIDE_FROM_ABI static constexpr auto
+  operator()(_Args&&... __args) noexcept(noexcept(std::invoke(_Fn, std::forward<_Args>(__args)...)))
+      -> decltype(std::invoke(_Fn, std::forward<_Args>(__args)...)) {
+    return std::invoke(_Fn, std::forward<_Args>(__args)...);
+  }
+};
+
+template <auto _Fn, class... _Args>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto bind_front(_Args&&... __args) {
+  static_assert((is_constructible_v<decay_t<_Args>, _Args> && ...),
+                "bind_front requires all decay_t<Args> to be constructible from respective Args");
+  static_assert((is_move_constructible_v<decay_t<_Args>> && ...),
+                "bind_front requires all decay_t<Args> to be move constructible");
+  if constexpr (using _Ty = decltype(_Fn); is_pointer_v<_Ty> || is_member_pointer_v<_Ty>)
+    static_assert(_Fn != nullptr, "f cannot be equal to nullptr");
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huixie90 wrote:

Perhaps mention `bind_front` in the message as you did in other messages?
Could we have a verify test where we pass a nullptr and this static assertion triigered?

https://github.com/llvm/llvm-project/pull/165096