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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Generic default parameters
Date: 11 May 2002 10:29:50 +0100
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Date: 2002-05-11T10:29:50+01:00
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"Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> writes:

> 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 think what you're discussing here is related to "traits" in the C++
world??? (something that's a black mystery to me). Or perhaps it's
"partial specialization".

Anyway, this would be very useful, I think, in simplifying a complex
generic arrangement like the BCs'.