factory constructor Typography

Source

factory Typography({ @required TargetPlatform platform }) {
  assert(platform != null);
  switch (platform) {
    case TargetPlatform.android:
    case TargetPlatform.fuchsia:
      return const Typography._(
          const TextTheme._blackMountainView(),
          const TextTheme._whiteMountainView(),
      );
    case TargetPlatform.iOS:
      return const Typography._(
          const TextTheme._blackCupertino(),
          const TextTheme._whiteCupertino(),
      );
  }
  return null;
}