resolve method
- TextDirection? direction
 
override
    Convert this instance into a BorderRadius, so that the radii are expressed for specific physical corners (top-left, top-right, etc) rather than in a direction-dependent manner.
See also:
- BorderRadius, for which this is a no-op (returns itself).
 - BorderRadiusDirectional, which flips the horizontal direction
based on the 
directionargument. 
Implementation
@override
BorderRadius resolve(TextDirection? direction) {
  assert(debugCheckCanResolveTextDirection(direction, '$BorderRadiusDirectional'));
  switch (direction!) {
    case TextDirection.rtl:
      return BorderRadius.only(
        topLeft: topEnd,
        topRight: topStart,
        bottomLeft: bottomEnd,
        bottomRight: bottomStart,
      );
    case TextDirection.ltr:
      return BorderRadius.only(
        topLeft: topStart,
        topRight: topEnd,
        bottomLeft: bottomStart,
        bottomRight: bottomEnd,
      );
  }
}