NOT INTENDED FOR LANDING: A promises demo

components/scheduler/promises/rejectable.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_SCHEDULER_PROMISES_REJECTABLE_H_
+#define COMPONENTS_SCHEDULER_PROMISES_REJECTABLE_H_
+
+#include "components/scheduler/scheduler_export.h"
+#include "components/scheduler/promises/template_helpers.h"
+
+namespace promise {
+namespace internal {
+template <typename ResolveT>
+class Resolve {
+ public:
+  explicit Resolve(const ResolveT& resolved) : resolved_(resolved) {}
+  explicit Resolve(ResolveT&& resolved) : resolved_(std::move(resolved)) {}
+
+  ResolveT resolved() const { return resolved_; }
+
+ private:
+  ResolveT resolved_;
+};
+
+template <>
+class Resolve<void> {
+ public:
+  Resolve() {}
+};
+
+template <typename RejectT>
+class Reject {
+ public:
+  explicit Reject(const RejectT& reject_reason)
+      : reject_reason_(reject_reason) {}
+
+  explicit Reject(RejectT&& reject_reason)
+      : reject_reason_(std::move(reject_reason)) {}
+
+  RejectT reject_reason() const { return reject_reason_; }
+
+ private:
+  RejectT reject_reason_;
+};
+
+template <>
+class Reject<void> {
+ public:
+  Reject() {}
+};
+
+}  // namespace internal
+
+// Syntatic sugar for Reject() and Resolve()
+template <typename ResolveT>
+internal::Resolve<ResolveT> Resolve(ResolveT resolved) {
+  return internal::Resolve<ResolveT>(std::move(resolved));
+}
+
+inline internal::Resolve<void> Resolve() {
+  return internal::Resolve<void>();
+}
+
+template <typename RejectT>
+internal::Reject<RejectT> Reject(RejectT reject_reason) {
+  return internal::Reject<RejectT>(std::move(reject_reason));
+}
+
+inline internal::Reject<void> Reject() {
+  return internal::Reject<void>();
+}
+
+class BaseRejectable {
+ public:
+  enum class State { UNRESOLVED, RESOLVED, REJECTED };
+
+  explicit BaseRejectable(State state) : state_(state) {}
+
+  bool is_rejected() const { return state_ == State::REJECTED; }
+  bool is_resolved() const { return state_ == State::RESOLVED; }
+  bool is_unresolved() const { return state_ == State::UNRESOLVED; }
+
+ protected:
+  State state_;
+};
+
+template <typename ResolveT, typename RejectT>
+class Rejectable : public BaseRejectable {
+ public:
+  Rejectable() : BaseRejectable(State::UNRESOLVED) {}
+
+  Rejectable(const internal::Resolve<ResolveT>& resolved)
+      : BaseRejectable(State::RESOLVED),
+        resolved_(std::move(resolved.resolved())) {}
+
+  Rejectable(const internal::Reject<RejectT>& resolved)
+      : BaseRejectable(State::REJECTED),
+        reject_reason_(std::move(resolved.reject_reason())) {}
+
+  ResolveT& resolved() {
+    DCHECK(is_resolved());
+    return resolved_;
+  }
+
+  RejectT& reject_reason() {
+    DCHECK(is_rejected());
+    return reject_reason_;
+  }
+
+  void Resolve(const ResolveT& resolved) {
+    resolved_ = resolved;
+    BaseRejectable::state_ = BaseRejectable::State::RESOLVED;
+  }
+
+  void Resolve(ResolveT&& resolved) {
+    resolved_ = std::move(resolved);
+    BaseRejectable::state_ = BaseRejectable::State::RESOLVED;
+  }
+
+  void Reject(const RejectT& reject_reason) {
+    reject_reason_ = reject_reason;
+    BaseRejectable::state_ = BaseRejectable::State::REJECTED;
+  }
+
+  void Reject(RejectT&& reject_reason) {
+    reject_reason_ = std::move(reject_reason);
+    BaseRejectable::state_ = BaseRejectable::State::REJECTED;
+  }
+
+ private:
+  ResolveT resolved_;
+  RejectT reject_reason_;
+};
+
+template <typename ResolveT>
+class Rejectable<ResolveT, void> : public BaseRejectable {
+ public:
+  Rejectable() : BaseRejectable(State::UNRESOLVED) {}
+
+  Rejectable(const internal::Resolve<ResolveT>& resolved)
+      : BaseRejectable(State::RESOLVED),
+        resolved_(std::move(resolved.resolved())) {}
+
+  Rejectable(const internal::Reject<void>& resolved)
+      : BaseRejectable(State::REJECTED) {}
+
+  ResolveT& resolved() {
+    DCHECK(is_resolved());
+    return resolved_;
+  }
+
+  void Resolve(const ResolveT& resolved) {
+    resolved_ = resolved;
+    BaseRejectable::state_ = BaseRejectable::State::RESOLVED;
+  }
+
+  void Resolve(ResolveT&& resolved) {
+    resolved_ = std::move(resolved);
+    BaseRejectable::state_ = BaseRejectable::State::RESOLVED;
+  }
+
+  void Reject() { BaseRejectable::state_ = BaseRejectable::State::REJECTED; }
+
+ private:
+  ResolveT resolved_;
+  bool is_rejected_;
+};
+
+template <typename RejectT>
+class Rejectable<void, RejectT> : public BaseRejectable {
+ public:
+  Rejectable() : BaseRejectable(State::UNRESOLVED) {}
+
+  Rejectable(const internal::Resolve<void>& resolved)
+      : BaseRejectable(State::RESOLVED) {}
+
+  Rejectable(const internal::Reject<RejectT>& resolved)
+      : BaseRejectable(State::REJECTED),
+        reject_reason_(std::move(resolved.reject_reason())) {}
+
+  RejectT& reject_reason() {
+    DCHECK(is_rejected());
+    return reject_reason_;
+  }
+
+  void Resolve() { BaseRejectable::state_ = BaseRejectable::State::RESOLVED; }
+
+  void Reject(const RejectT& reject_reason) {
+    reject_reason_ = reject_reason;
+    BaseRejectable::state_ = BaseRejectable::State::REJECTED;
+  }
+
+  void Reject(RejectT&& reject_reason) {
+    reject_reason_ = std::move(reject_reason);
+    BaseRejectable::state_ = BaseRejectable::State::REJECTED;
+  }
+
+ private:
+  RejectT reject_reason_;
+};
+
+template <>
+class Rejectable<void, void> : public BaseRejectable {
+ public:
+  Rejectable() : BaseRejectable(State::UNRESOLVED) {}
+
+  Rejectable(const internal::Resolve<void>& resolved)
+      : BaseRejectable(State::RESOLVED) {}
+
+  Rejectable(const internal::Reject<void>& resolved)
+      : BaseRejectable(State::REJECTED) {}
+
+  void Resolve() { BaseRejectable::state_ = BaseRejectable::State::RESOLVED; }
+
+  void Reject() { BaseRejectable::state_ = BaseRejectable::State::REJECTED; }
+};
+
+// Similar to std::enable_if but used to detect if a template parameter is a
+// Rejectable<>.
+template <typename R, class ResultT = void>
+struct enable_if_rejectable {};
+
+template <typename ResolveT, typename RejectT, class ResultT>
+struct enable_if_rejectable<Rejectable<ResolveT, RejectT>, ResultT> {
+  typedef ResultT type;
+};
+
+}  // namespace promise
+
+#endif  // COMPONENTS_SCHEDULER_PROMISES_REJECTABLE_H_