[MUD-Dev] Object Models

[Miroslav Silovic]

"John Buehler" <johnbue at msn.com> writes:

> To me, runtime type checking implies the possibility of a piece of
> code getting its hands on a component that is supposed to be type A,
> but in fact it is type B.  Static type checking is intended to
> ensure that this situation does not take place because the component
> is known to be type B and, therefore, cannot be passed to the code
> which has declared itself to accept only type A components.

This is so easy to catch by testing that it's almost irrelevant. The
assertions failures are the real source of errors in any interesting
piece of code.

> Your mention of verification of pre- and post-conditions, class
> invariants and such suggests to me that you consider this to be
> related to type checking.  It is, after a fashion, but we were doing
> those things up front.  So we would define precise contracts,
> implement components and then verify those components against those
> contracts by actually running the component exhaustively and
> verifying that the contracts were adhered to.  Once that process is
> completed, the component is declared to be of type X and is shipped.

Yes, well, type is a set of objects satifying certain conditions. So a
set of objects that satisfy a precondition is also a type, by this
definition (I know of at least two programming languages that don't
make a distiction between a type and a constraint).

So you're telling me that you -still- check your types by testing,
which is precisely my argument.

> > Whenever I use strong typing, I'm left with an impression that I spend
> > lots of effort declaring things for VERY little gain - this is because
> > most of my errors end up having nothing to do with anything that can
> > be statically checked.
> 
> This really throws me a curve.  What errors are we talking about?

I meant 'bugs' here.

--
How to eff the ineffable?
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