cast<T extends Dimension> method
Casts this unit to dim.
Throws if the dimensions are incompatible.
Implementation
Unit<T> cast<T extends Dimension>(T dim) {
if (this is Unit<T> && dim.isCompatible(this.dim)) return (this as Unit<T>);
if (dim.isMine(this)) return Unit<T>(dim, symbol, name: name, converter: converter);
throw 'Incompatible dimension';
}