chromium/third_party/grpc/src/src/core/lib/promise/loop.h

// 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_LOOP_H
#define GRPC_SRC_CORE_LIB_PROMISE_LOOP_H

#include <grpc/support/port_platform.h>

#include <new>
#include <type_traits>
#include <utility>

#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/types/variant.h"

#include "src/core/lib/promise/detail/promise_factory.h"
#include "src/core/lib/promise/poll.h"

namespace grpc_core {

// Special type - signals to loop to take another iteration, instead of
// finishing
struct Continue { … };

// Result of polling a loop promise - either Continue looping, or return a value
// T
LoopCtl;

namespace promise_detail {

template <typename T>
struct LoopTraits;

LoopTraits<LoopCtl<T>>;

LoopTraits<absl::StatusOr<LoopCtl<T>>>;

template <>
struct LoopTraits<absl::StatusOr<LoopCtl<absl::Status>>> { … };

template <typename F>
class Loop { … };

}  // namespace promise_detail

// Looping combinator.
// Expects F returns LoopCtl<T> - if it's Continue, then run the loop again -
// otherwise yield the returned value as the result of the loop.
template <typename F>
promise_detail::Loop<F> Loop(F f) { … }

}  // namespace grpc_core

#endif  // GRPC_SRC_CORE_LIB_PROMISE_LOOP_H