Directionality constructor

const Directionality({Key key, @required TextDirection textDirection, @required Widget child })

Creates a widget that determines the directionality of text and text-direction-sensitive render objects.

The textDirection and child arguments must not be null.

Implementation 

const Directionality({
  Key key,
  @required this.textDirection,
  @required Widget child
}) : assert(textDirection != null),
     assert(child != null),
     super(key: key, child: child);