On Tue, Oct 01, 2002 at 02:49:49PM -0700, Michael Lazzaro wrote:
> >>My musing is that the behavior of a class in different contexts is
> >>itself an interface, in the sense of being a contract between a
> >>class/subclass and it's users
> >
> >Ah HA! Contract! Return values can be enforce via a simple DBC post
> >condition, no need to invent a whole new return value signature.
>
> I think I get it, but can you give some pseudocode? If you want a
> method to return a list of Zoo animals in "list" context, and a Zoo
> object in "Zoo object" context, what would that look like?
The trick is having some way of getting at the return value. Class::Contract
does this by having a magic value() function you can call in a
post-condition. I can't think of anything better, so...
class Animals;
method zoo {
...
# I have no idea what actual post condition syntax will look like
post {
given want {
when 'LIST' { grep { $^thing.isa('Zoo::Animal') } value() }
default { value().isa('Zoo') }
}
}
}
It might be nice if the return value was the topic of the post condition,
but that leads to problems of how you deal with lists as topics which I
don't know if they've been solved.
> (I'm assuming that DBC postconditions on a method would be treated,
> internally, as part of the overall signature/prototype of the method:
> i.e. if you override the method in a subclass, all original
> postconditions would still remain attached to it (though the new method
> might itself add additional postconditions.))
That's how I understand it works.
--
Michael G. Schwern <[EMAIL PROTECTED]> http://www.pobox.com/~schwern/
Perl Quality Assurance <[EMAIL PROTECTED]> Kwalitee Is Job One
I'm a man, but I can change... if I have to.
-- Red Green
