// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

/**
 * Indicates that loading of [libraryName] is deferred.
 *
 * Applies to library imports, when used as metadata.
 *
 * Example usage:
 *
 * [:
 * @lazy
 * import 'foo.dart' as foo;
 *
 * const lazy = const DeferredLibrary('com.example.foo');
 *
 * void main() {
 *   foo.method(); // Throws a NoSuchMethodError, foo is not loaded yet.
 *   lazy.load().then(onFooLoaded);
 * }
 *
 * void onFooLoaded(_) {
 *   foo.method();
 * }
 * :]
 */
class DeferredLibrary {
  final String libraryName;
  final String uri;

  const DeferredLibrary(this.libraryName, {this.uri});

  /**
   * Ensure that [libraryName] has been loaded.
   *
   * The value of the returned future is true if this invocation of
   * [load] caused the library to be loaded.
   */
  external Future<bool> load();
}