Re: 7.0 wishlist?

On Nov 13, 5:48 pm, Andreas Leitgeb <a...@xxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Joshua Cranmer <Pidgeo...@xxxxxxxxxxxxxxx> wrote:
Note, for example, that
making a Square class extend a Rectangle (since a Square is-a Rectangle)
does not actually work since it would fail to match the Rectangle's
contract.

I may not understand your example in all its possible deepness, but
what type of rectangle-related contract do you have in mind, that is
not met by a square?  I hope it is not something like "width!=height
must be allowed": such types of contracts would thwart almost every
"is-a" relation.

Square is-a rectangle doesn't work for mutable types: if you modify
the width of a rectangle, the contract is not such that the height may
change as well. Square is-a rectangle works fine for immutable types
and for case classes; in the former case, Square only expands the API
and replaces the constructor, and in the latter, modifying the
dimensions makes the object not-a Square any more (but still a
Rectangle).

Shapes and Animals are still stupid examples, mind.

-o
.

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