Roll forward to cl/314747126

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: Ie19e006429b138b3768e97dae971a43fdc5ef8bf

cpp/platform_v2/base/callable.h

@@ -0,0 +1,37 @@
+// Copyright 2020 Google LLC
+//
+// 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
+//
+//     https://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 PLATFORM_V2_BASE_CALLABLE_H_
+#define PLATFORM_V2_BASE_CALLABLE_H_
+
+#include <functional>
+
+#include "platform_v2/base/exception.h"
+
+namespace location {
+namespace nearby {
+
+// The Callable is and object intended to be executed by a thread, that is able
+// to return a value of specified type T.
+// It must be invokable without arguments. It must return a value implicitly
+// convertible to ExceptionOr<T>.
+//
+// https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Callable.html
+template <typename T>
+using Callable = std::function<ExceptionOr<T>()>;
+
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_V2_BASE_CALLABLE_H_