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// Copyright 2026 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Implementation details for `absl::bind_back()`.
#ifndef ABSL_FUNCTIONAL_INTERNAL_BACK_BINDER_H_
#define ABSL_FUNCTIONAL_INTERNAL_BACK_BINDER_H_
#include <cstddef>
#include <type_traits>
#include <utility>
#include "absl/base/config.h"
#include "absl/container/internal/compressed_tuple.h"
#include "absl/utility/utility.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace functional_internal {
// Invoke the method, expanding the tuple of bound arguments.
template <class R, class Tuple, size_t... Idx, class... Args>
constexpr R ApplyBack(Tuple&& bound, std::index_sequence<Idx...>,
Args&&... free) {
return std::invoke(std::forward<Tuple>(bound).template get<0>(),
std::forward<Args>(free)...,
std::forward<Tuple>(bound).template get<Idx + 1>()...);
}
template <class F, class... BoundArgs>
class BackBinder {
using BoundArgsT = absl::container_internal::CompressedTuple<F, BoundArgs...>;
using Idx = std::make_index_sequence<sizeof...(BoundArgs)>;
BoundArgsT bound_args_;
public:
template <class... Ts>
constexpr explicit BackBinder(std::in_place_t, Ts&&... ts)
: bound_args_(std::forward<Ts>(ts)...) {}
template <class... FreeArgs,
class R = std::invoke_result_t<F&, FreeArgs&&..., BoundArgs&...>>
constexpr R operator()(FreeArgs&&... free_args) & {
return functional_internal::ApplyBack<R>(
bound_args_, Idx(), std::forward<FreeArgs>(free_args)...);
}
template <class... FreeArgs,
class R = std::invoke_result_t<const F&, FreeArgs&&...,
const BoundArgs&...>>
constexpr R operator()(FreeArgs&&... free_args) const& {
return functional_internal::ApplyBack<R>(
bound_args_, Idx(), std::forward<FreeArgs>(free_args)...);
}
template <class... FreeArgs,
class R = std::invoke_result_t<F&&, FreeArgs&&..., BoundArgs&&...>>
constexpr R operator()(FreeArgs&&... free_args) && {
// This overload is called when *this is an rvalue. If some of the bound
// arguments are stored by value or rvalue reference, we move them.
return functional_internal::ApplyBack<R>(
std::move(bound_args_), Idx(), std::forward<FreeArgs>(free_args)...);
}
template <class... FreeArgs,
class R = std::invoke_result_t<const F&&, FreeArgs&&...,
const BoundArgs&&...>>
constexpr R operator()(FreeArgs&&... free_args) const&& {
// This overload is called when *this is an rvalue. If some of the bound
// arguments are stored by value or rvalue reference, we move them.
return functional_internal::ApplyBack<R>(
std::move(bound_args_), Idx(), std::forward<FreeArgs>(free_args)...);
}
};
template <class F, class... BoundArgs>
using bind_back_t = BackBinder<std::decay_t<F>, std::decay_t<BoundArgs>...>;
} // namespace functional_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_FUNCTIONAL_INTERNAL_BACK_BINDER_H_
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