OffsetBase constructor Null safety

const OffsetBase(
  1. double _dx,
  2. double _dy

Abstract const constructor. This constructor enables subclasses to provide const constructors so that they can be used in const expressions.

The first argument sets the horizontal component, and the second the vertical component.


const OffsetBase(this._dx, this._dy)
    : assert(_dx != null),
      assert(_dy != null);