Skeleton API for lazy library loading.

dart/sdk/lib/async/deferred_load.dart

Index: dart/sdk/lib/async/deferred_load.dart
diff --git a/dart/sdk/lib/async/deferred_load.dart b/dart/sdk/lib/async/deferred_load.dart
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+// 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

[floitsch, 2013/02/18 14:51:02]

I would follow some convention (as Kasper suggested).
for example:
@lazyFooLibrary

[ahe, 2013/02/18 15:20:28]

As I implied to Kasper, I'm not keen on setting precedent. Calling this "lazy"
doesn't work if you have multiple libraries, so people need to come up with
different conventions. Once the debate has settled down, I'll be happy to
approve a CL to change this comment.

+ * 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();
+}