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/base/internal/invoke.h"
25 #include "absl/container/internal/compressed_tuple.h"
26 #include "absl/meta/type_traits.h"
27 #include "absl/utility/utility.h"
28
29 namespace absl {
30 ABSL_NAMESPACE_BEGIN
31 namespace functional_internal {
32
33 // Invoke the method, expanding the tuple of bound arguments.
34 template <class R, class Tuple, size_t... Idx, class... Args>
Apply(Tuple && bound,absl::index_sequence<Idx...>,Args &&...free)35 R Apply(Tuple&& bound, absl::index_sequence<Idx...>, Args&&... free) {
36 return base_internal::invoke(
37 absl::forward<Tuple>(bound).template get<Idx>()...,
38 absl::forward<Args>(free)...);
39 }
40
41 template <class F, class... BoundArgs>
42 class FrontBinder {
43 using BoundArgsT = absl::container_internal::CompressedTuple<F, BoundArgs...>;
44 using Idx = absl::make_index_sequence<sizeof...(BoundArgs) + 1>;
45
46 BoundArgsT bound_args_;
47
48 public:
49 template <class... Ts>
FrontBinder(absl::in_place_t,Ts &&...ts)50 constexpr explicit FrontBinder(absl::in_place_t, Ts&&... ts)
51 : bound_args_(absl::forward<Ts>(ts)...) {}
52
53 template <class... FreeArgs, class R = base_internal::invoke_result_t<
54 F&, BoundArgs&..., FreeArgs&&...>>
operator()55 R operator()(FreeArgs&&... free_args) & {
56 return functional_internal::Apply<R>(bound_args_, Idx(),
57 absl::forward<FreeArgs>(free_args)...);
58 }
59
60 template <class... FreeArgs,
61 class R = base_internal::invoke_result_t<
62 const F&, const BoundArgs&..., FreeArgs&&...>>
operator()63 R operator()(FreeArgs&&... free_args) const& {
64 return functional_internal::Apply<R>(bound_args_, Idx(),
65 absl::forward<FreeArgs>(free_args)...);
66 }
67
68 template <class... FreeArgs, class R = base_internal::invoke_result_t<
69 F&&, BoundArgs&&..., FreeArgs&&...>>
operator()70 R operator()(FreeArgs&&... free_args) && {
71 // This overload is called when *this is an rvalue. If some of the bound
72 // arguments are stored by value or rvalue reference, we move them.
73 return functional_internal::Apply<R>(absl::move(bound_args_), Idx(),
74 absl::forward<FreeArgs>(free_args)...);
75 }
76
77 template <class... FreeArgs,
78 class R = base_internal::invoke_result_t<
79 const F&&, const BoundArgs&&..., FreeArgs&&...>>
operator()80 R operator()(FreeArgs&&... free_args) const&& {
81 // This overload is called when *this is an rvalue. If some of the bound
82 // arguments are stored by value or rvalue reference, we move them.
83 return functional_internal::Apply<R>(absl::move(bound_args_), Idx(),
84 absl::forward<FreeArgs>(free_args)...);
85 }
86 };
87
88 template <class F, class... BoundArgs>
89 using bind_front_t = FrontBinder<decay_t<F>, absl::decay_t<BoundArgs>...>;
90
91 } // namespace functional_internal
92 ABSL_NAMESPACE_END
93 } // namespace absl
94
95 #endif // ABSL_FUNCTIONAL_INTERNAL_FRONT_BINDER_H_
96