Re: Generic default parameters

["Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org>]

The original issue was one of bringing in a "Count Of List Elements" type as
a generic parameter. You have to bring in the element type because you can't
know what that should be in advance. However, you *might* want to say
"Unless Otherwise Directed Make The Count Of List Elements Be 'Natural'" -
the reason being that for a large number of simple cases, you may never want
anything more specialized than Natural - so you don't want the extra work of
specifying it in the instantiation. Yet you want the ability to override the
default from time to time if for some reason you *do* want a more
specialized type. Example:

generic
    type Element_Type is private ;
    type Element_Count is range <> => Natural ; -- or whatever syntax
package Lists is.....

and then....

package My_Simple_Lists is new Lists (Element_Type => Some_Type);

(Here I got a list that will be counted up with Natural)

package
    My_Really_Strongly_Typed_Lists
is new
    Lists (
        Element_Type => Apple_Type,
        Element_Count =>
Apple_Counter_Not_To_Be_Confused_With_Apple_Cart_Pushers_Counters);

The idea is to let the obsessive-compulsives get what they want without
bumming out the laid-back, chilling dudes for whom Natural is good enough.
:-)

From here, I might imagine a case where for a more complex generic parameter
list, I might have half of the parameters have defaults the other half are
"must supply" parameters. Think of when you might have a function or
procedure in which you have default values for parameters. Same thing.

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com


"Preben Randhol" <randhol+abuse@pvv.org> wrote in message
news:slrnadq3j5.1cf.randhol+abuse@kiuk0156.chembio.ntnu.no...
>
> 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 :-)
>