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Date: Wed, 12 Dec 2007 13:37:09 +0200
From: Niklas Holsti <niklas.holsti@tidorum.invalid>
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Newsgroups: comp.lang.ada
Subject: Re: Exceptions
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Date: 2007-12-12T13:37:09+02:00
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Randy Brukardt wrote:
> "Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message
> news:475e8bde$0$27850$4f793bc4@news.tdc.fi...
> ...
> 
>>And perhaps also
>>
>>   5. Exceptions as formal generic parameters.
> 
> 
> Ada has this (although it isn't obvious): just pass an
> Ada.Exceptions.Exception_Id to the generic. That is, given a generic spec
> something like:
> 
>     generic
>          My_Exception : Ada.Exceptions.Exception_Id :=
> Constraint_Error'Identity;
>     package Gen is ...

Ha, a good technique to know, thanks.

> In any case, the fact that it is relatively easy to do this is why there is
> no formal exception parameter.

If the implementation with Exception_Id is so easy, I wonder that 
the syntax with "exception" as formal parameter is not included in 
the language. But I know that language extensions are prioritized, 
and in fact I have never needed a formal exception parameter, 
although I have sometimes written wrappers for instances of 
generics just to translate an exception defined and raised by the 
generic into some other exception for the user of the generic.

In any plan to extend Ada with exception contracts, I think that 
formal exception parameters should be included, or else the 
contract should allow exceptions to be named by Exception_Id as 
well as by the lexical identifier.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .