You seem to be saying that circles are not subtypes of ellipses. That circleness...

davidmathers on Sept 15, 2009 | parent | context | favorite | on: A Square Is Not A Rectangle

You seem to be saying that circles are not subtypes of ellipses. That circleness is just a property of ellipses. If we accept that then the whole issue is moot, and substitutability is true by tautology.

A circle is a triple: (x,y,radius). An ellipse is a 5-tuple: (x,y,major,minor,angle).

Maybe we should be talking about angle instead? It can't be derived from a circle. What happens when you feed a circle to selectEllipsesByAngle()?

barrkel on Sept 16, 2009 [–]

If isEllipseAtAngle(someAngle): boolean were a method, a Circle type could return true for every angle.