Re: Types for Perl 6: request for comments

Now that I've read ahead to 3.4, the "multi method solution" shown can be a
little simpler, just need to add "multi" to the original "equal" methods,
see attached.

-y

On Tue, Jun 30, 2015 at 4:16 PM, yary <[email protected]> wrote:

> Section 3.2's example does not fail for the given reason "This tries to
> access the c instance variable of the argument $b thus yielding a
> run-time error" - instead Perl6 more correctly complains that it was
> expecting a ColPoint, but got a Point instead. Indeed one cannot generally
> replace a subtype with its parent type, only the other way around. Can
> correct by re-writing along the lines of "This fails to dispatch because
> ColPoint's equal method requires a ColPoint argument, but we are calling
> it with the supertype Point, which does not compose with the method's
> signature."
>
> (Furthermore if "equal" is defined as a "multi method," then the
> dispatcher chooses Point's "equal" method, and the example returns
> "True," which all looks good to me. But it doesn't illustrate the paper's
> point.)
>
> -y
>
>