front_binder.h (3599B)
1 // Copyright 2018 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 // Implementation details for `absl::bind_front()`. 16 17 #ifndef ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_ 18 #define ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_ 19 20 #include <cstddef> 21 #include <type_traits> 22 #include <utility> 23 24 #include "absl/container/internal/compressed_tuple.h" 25 #include "absl/meta/type_traits.h" 26 #include "absl/utility/utility.h" 27 28 namespace absl { 29 ABSL_NAMESPACE_BEGIN 30 namespace functional_internal { 31 32 // Invoke the method, expanding the tuple of bound arguments. 33 template <class R, class Tuple, size_t... Idx, class... Args> 34 R Apply(Tuple&& bound, absl::index_sequence<Idx...>, Args&&... free) { 35 return std::invoke(std::forward<Tuple>(bound).template get<Idx>()..., 36 std::forward<Args>(free)...); 37 } 38 39 template <class F, class... BoundArgs> 40 class FrontBinder { 41 using BoundArgsT = absl::container_internal::CompressedTuple<F, BoundArgs...>; 42 using Idx = absl::make_index_sequence<sizeof...(BoundArgs) + 1>; 43 44 BoundArgsT bound_args_; 45 46 public: 47 template <class... Ts> 48 constexpr explicit FrontBinder(absl::in_place_t, Ts&&... ts) 49 : bound_args_(std::forward<Ts>(ts)...) {} 50 51 template <class... FreeArgs, 52 class R = std::invoke_result_t<F&, BoundArgs&..., FreeArgs&&...>> 53 R operator()(FreeArgs&&... free_args) & { 54 return functional_internal::Apply<R>(bound_args_, Idx(), 55 std::forward<FreeArgs>(free_args)...); 56 } 57 58 template <class... FreeArgs, 59 class R = std::invoke_result_t<const F&, const BoundArgs&..., 60 FreeArgs&&...>> 61 R operator()(FreeArgs&&... free_args) const& { 62 return functional_internal::Apply<R>(bound_args_, Idx(), 63 std::forward<FreeArgs>(free_args)...); 64 } 65 66 template <class... FreeArgs, 67 class R = std::invoke_result_t<F&&, BoundArgs&&..., FreeArgs&&...>> 68 R operator()(FreeArgs&&... free_args) && { 69 // This overload is called when *this is an rvalue. If some of the bound 70 // arguments are stored by value or rvalue reference, we move them. 71 return functional_internal::Apply<R>(std::move(bound_args_), Idx(), 72 std::forward<FreeArgs>(free_args)...); 73 } 74 75 template <class... FreeArgs, 76 class R = std::invoke_result_t<const F&&, const BoundArgs&&..., 77 FreeArgs&&...>> 78 R operator()(FreeArgs&&... free_args) const&& { 79 // This overload is called when *this is an rvalue. If some of the bound 80 // arguments are stored by value or rvalue reference, we move them. 81 return functional_internal::Apply<R>(std::move(bound_args_), Idx(), 82 std::forward<FreeArgs>(free_args)...); 83 } 84 }; 85 86 template <class F, class... BoundArgs> 87 using bind_front_t = FrontBinder<decay_t<F>, absl::decay_t<BoundArgs>...>; 88 89 } // namespace functional_internal 90 ABSL_NAMESPACE_END 91 } // namespace absl 92 93 #endif // ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_