/*!
@mainpage Common Components for the Google Cloud C++ Client Libraries

# Overview

This library contains common components shared by all the Google Cloud C++
Client Libraries. Including:

- [Status](@ref google::cloud::v1::Status) error codes and details from an
  operation.
- [StatusOr<T>](@ref google::cloud::v1::StatusOr) returns a value on success
  and a `Status` on error.
- [future<T>](@ref google::cloud::v1::future) and
  [promise<T>](@ref google::cloud::v1::promise) futures (a holder that will
  receive a value asynchronously) and promises (the counterpart of a future,
  where values are stored asynchronously). They satisfy the API for
  `std::future` and `std::promise`, and add support for callbacks and
  cancellation.

@warning The symbols in the `google::cloud::internal` namespace are
implementation details and subject to change and/or removal without notice.

@warning The symbols in the `google::cloud::testing_util` namespace are
implementation details and subject to change and/or removal without notice.

*/