Re: Extension of non-limited type needs limited component

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> All that are more or less decoupled things. Why should we tie all of them 
               ^^^^^^^^^^^^
> under one roof?

Less, I'd say.  ;-)

They are all closely related to whether you can copy the thing.
To answer my question properly, you would have to explain exactly
when each of the things I mentioned should be allowed.  That's not
easy.  No, I don't expect anybody to do all that work for an informal
usenet discussion.  ;-)

>...[However, I am afraid, that to correctly deal with it one 
> would need multiple dispatch anyway.]

I like the idea of multi-dispatch, but all of the languages I've seen
that support it seem confusing and/or error-prone.  You need a rule that
makes it predictable which method(s) will be called in every case.  Not
just predictable in a formal sense, but predictable by mere mortal
programmers -- i.e. the programmer's guess should match what the
compiler actually does.  And you need a way to prevent ambiguities --
cases where two different methods are "reasonable" should be forbidden,
preferably at compile time.  And you need a way to organize the code --
with single dispatch, you can put the "methods" with the "type" (or
"class" or whatever).

- Bob