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// Copyright 2021 gRPC 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
//
// http://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.
#ifndef GRPC_SRC_CORE_LIB_PROMISE_DETAIL_PROMISE_LIKE_H
#define GRPC_SRC_CORE_LIB_PROMISE_DETAIL_PROMISE_LIKE_H
#include <grpc/support/port_platform.h>
#include <utility>
#include "absl/meta/type_traits.h"
#include "src/core/lib/promise/poll.h"
// A Promise is a callable object that returns Poll<T> for some T.
// Often when we're writing code that uses promises, we end up wanting to also
// deal with code that completes instantaneously - that is, it returns some T
// where T is not Poll.
// PromiseLike wraps any callable that takes no parameters and implements the
// Promise interface. For things that already return Poll, this wrapping does
// nothing. For things that do not return Poll, we wrap the return type in Poll.
// This allows us to write things like:
// Seq(
// [] { return 42; },
// ...)
// in preference to things like:
// Seq(
// [] { return Poll<int>(42); },
// ...)
// or:
// Seq(
// [] -> Poll<int> { return 42; },
// ...)
// leading to slightly more concise code and eliminating some rules that in
// practice people find hard to deal with.
namespace grpc_core {
namespace promise_detail {
template <typename T>
struct PollWrapper {
static Poll<T> Wrap(T&& x) { return Poll<T>(std::forward<T>(x)); }
};
template <typename T>
struct PollWrapper<Poll<T>> {
static Poll<T> Wrap(Poll<T>&& x) { return std::forward<Poll<T>>(x); }
};
template <typename T>
auto WrapInPoll(T&& x) -> decltype(PollWrapper<T>::Wrap(std::forward<T>(x))) {
return PollWrapper<T>::Wrap(std::forward<T>(x));
}
template <typename F, typename SfinaeVoid = void>
class PromiseLike;
template <>
class PromiseLike<void>;
// Android local modification: Android builds grpc with C++20, which removes
// std::result_of. Use std::invoke_result_t instead.
template <typename F>
class PromiseLike<F, absl::enable_if_t<!std::is_void<
#if __cplusplus >= 201703L
std::invoke_result_t<F>
#else
typename std::result_of<F()>::type
#endif
>::value>> {
private:
GPR_NO_UNIQUE_ADDRESS F f_;
public:
// NOLINTNEXTLINE - internal detail that drastically simplifies calling code.
PromiseLike(F&& f) : f_(std::forward<F>(f)) {}
auto operator()() -> decltype(WrapInPoll(f_())) { return WrapInPoll(f_()); }
using Result = typename PollTraits<decltype(WrapInPoll(f_()))>::Type;
};
// T -> T, const T& -> T
template <typename T>
using RemoveCVRef = absl::remove_cv_t<absl::remove_reference_t<T>>;
} // namespace promise_detail
} // namespace grpc_core
#endif // GRPC_SRC_CORE_LIB_PROMISE_DETAIL_PROMISE_LIKE_H
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