Re: Generic default parameters

[Preben Randhol <randhol+abuse@pvv.org>]

On Fri, 10 May 2002 12:50:52 -0400, Marin David Condic wrote:

> For the same reason that (in effect) you can have a "default value"
> for functions. You say you want a "<" function and with the "is <>"
> part you are saying, "But if one is already defined and you don't need
> to override it for any reason, then you can save yourself the
> effort."
> 
> In your example, this is fine for a generic where you want only one
> parameter to default (or all parameters to default). What if you have
> 5 parameters and only two of them can sensibly have a default? You
> can't pre-instantiate with just the two parameters. (Although this
> might pose a solution that requires no new syntax..... Hmmm......) In
> the case of Lists, the type of element you're storing should never
> default because it doesn't make sense. However the data type of a
> returned element count might sanely default to Natural unless the user
> has something else in mind. How would you pre-instantiate that with a
> default value when you have no default element type?

I'm not sure I understand. If you have 5 parameters and only two can
have a default then I don't see why giving the generic defaults would
help. To me it sounds like making generics less strongly typed/more
dynamic, but probably I misunderstand you :-)

Preben
--