Roll forward to cl/338482889

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: I9850950db8bd84f0904ea1a413151887f52098cf

cpp/platform/public/future.h

@@ -0,0 +1,44 @@
+#ifndef PLATFORM_PUBLIC_FUTURE_H_
+#define PLATFORM_PUBLIC_FUTURE_H_
+
+#include "platform/public/settable_future.h"
+
+namespace location {
+namespace nearby {
+
+template <typename T>
+class Future final {
+ public:
+  virtual bool Set(T value) { return impl_->Set(std::move(value)); }
+  virtual bool SetException(Exception exception) {
+    return impl_->SetException(exception);
+  }
+  virtual ExceptionOr<T> Get() { return impl_->Get(); }
+  virtual ExceptionOr<T> Get(absl::Duration timeout) {
+    return impl_->Get(timeout);
+  }
+  void AddListener(Runnable runnable, api::Executor* executor) {
+    impl_->AddListener(std::move(runnable), executor);
+  }
+  bool IsSet() const {
+    return impl_->IsSet();
+  }
+
+ private:
+  // Instance of future implementation is wrapped in shared_ptr<> to make
+  // it possible to pass Future by value and share the implementation.
+  // This allows for the following constructions:
+  // 1)
+  // Future<bool> future;
+  // RunOnXyzThread([future]() { future.Set(DoTheJobAndReport()); });
+  // if (future.Get().Ok()) { /*...*/ }
+  // 2)
+  // Future<bool> future = DoSomeAsyncWork(); // Returns future, but keeps copy.
+  // if (future.Get().Ok()) { /*...*/ }
+  std::shared_ptr<SettableFuture<T>> impl_{new SettableFuture<T>()};
+};
+
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_PUBLIC_FUTURE_H_