Jonathan Lang wrote:
In any case, one should never add
anything while going from specific to general.

The crux of my example is that one indeed adds methods
in the supertype. The subtype receives a standard
implementation. This pattern is applicable whenever
you have a case like the Num that can be embedded in
the Complex with .im == 0. Another example is deriving
a Point3D from a Point2D by giving a default
implementation of .z == 0.

Regards, TSa.

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