once_function.h

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/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
 
#pragma once
 
#include <utility>
 
#include <dispenso/detail/once_callable_impl.h>
#include <dispenso/platform.h>
 
namespace dispenso {
 
#if DISPENSO_HAS_CONCEPTS
template <typename F>
concept OnceCallableFunc = std::invocable<F>;
#endif // DISPENSO_HAS_CONCEPTS
 
namespace detail {
template <typename Result>
class FutureBase;
template <typename Result>
class FutureImplBase;
} // namespace detail
 
class OnceFunction {
 public:
  OnceFunction()
#if defined DISPENSO_DEBUG
      : onceCallable_(nullptr)
#endif // DISPENSO_DEBUG
  {
  }
 
  template <typename F>
  DISPENSO_REQUIRES(OnceCallableFunc<F>)
  OnceFunction(F&& f) : onceCallable_(detail::createOnceCallable(std::forward<F>(f))) {}
 
  OnceFunction(const OnceFunction& other) = delete;
 
  OnceFunction(OnceFunction&& other) : onceCallable_(other.onceCallable_) {
#if defined DISPENSO_DEBUG
    other.onceCallable_ = nullptr;
#endif // DISPENSO_DEBUG
  }
 
  OnceFunction& operator=(OnceFunction&& other) {
    onceCallable_ = other.onceCallable_;
#if defined DISPENSO_DEBUG
    if (&other != this) {
      other.onceCallable_ = nullptr;
    }
#endif // DISPENSO_DEBUG
    return *this;
  }
 
  void operator()() const {
#if defined DISPENSO_DEBUG
    assert(onceCallable_ != nullptr && "Must not use OnceFunction more than once!");
#endif // DISPENSO_DEBUG
 
    onceCallable_->run();
 
#if defined DISPENSO_DEBUG
    onceCallable_ = nullptr;
#endif // DISPENSO_DEBUG
  }
 
 private:
  OnceFunction(detail::OnceCallable* func, bool) : onceCallable_(func) {}
 
  mutable detail::OnceCallable* onceCallable_;
 
  template <typename Result>
  friend class detail::FutureBase;
  template <typename Result>
  friend class detail::FutureImplBase;
};
 
} // namespace dispenso