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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: stopping a loop iteration without exiting it
Date: Sun, 7 Jan 2018 13:27:43 +0100
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Xref: reader02.eternal-september.org comp.lang.ada:49803
Date: 2018-01-07T13:27:43+01:00
List-Id: <comp.lang.ada>

On 2018-01-07 12:52, Niklas Holsti wrote:
> On 18-01-04 23:17 , Dmitry A. Kazakov wrote:
> 
>> I thought about really important cases, but could not invent syntax:
>>
>>    if X in T'Class then
>>       declare
>>          Same_X : T'Class renames T'Class (X);
>>       begin
>>          ...
>>       end;
>>    end if;
> 
> I suggested and we discussed a form of "case" statement as new syntax 
> for this. Here is another syntax suggestion using the keyword "is" to 
> form a new kind of membership test, which also assigns a new name to the 
> object when the test succeeds:
> 
>     if X is Same_X : T'Class then
>        ...
>     end if;
> 
> Another form, retaining the "in", could be
> 
>     if X is Same_X in T'Class then
>        ...
>     end if;

I think keeping colon in declarations is important.

>>    if P /= null then
>>       declare
>>          X : P_Type renames P.all;
>>       begin
>>          ...
>>       end;
>>    end if;
> 
>     if P.all is X : P_Type then
>        ...
>     end if;
> 
> where there would have to be a rule that the membership test is false if 
> P is null, without raising Constraint_Error.

Or ".all" just dropped as in the cases like array indexing.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de