What is a type error?

[Marshall]

Chris Smith wrote:
>
> But this starts to look bad, because we used to have this nice property
> called encapsulation.  To work around that, we'd need to make one of a
> few choices: (a) give up encapsulation, which isn't too happy; (b) rely
> on type inference for this kind of stuff, and consider it okay if the
> type inference system breaks encapsulation; or (c) invent some kind of
> generic constraint language so that constraints like this could be
> expressed without exposing field names.  Choice (b) is incomplete, as
> there will often be times when I need to ascribe a type to a parameter
> or some such thing, and the lack of ability to express the complete type
> system will be rather limiting.  Choice (c), though, looks a little
> daunting.

Damn the torpedoes, give me choice c!

I've been saying for a few years now that encapsulation is only
a hack to get around the lack of a decent declarative constraint
language.


Marshall