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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: About String
Newsgroups: comp.lang.ada
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Date: Mon, 9 Jun 2008 12:25:02 +0200
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Date: 2008-06-09T12:25:02+02:00
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On Mon, 09 Jun 2008 11:43:36 +0200, Georg Bauhaus wrote:

> Dmitry A. Kazakov schrieb:

>> On Sun, 08 Jun 2008 17:19:11 -0400, Robert A Duff wrote:
>> 
>>> Maciej Sobczak <see.my.homepage@gmail.com> writes:
>>>
>>>> After all, with the possibility to initialize the new variable with
>>>> arbitrarily complex expression (including function call), this is
>>>> already the case and the whole declare-begin-end block is just
>>>> reflecting some artificial separation.

>>> I agree.  I suppose it comes from Pascal, where declarations and
>>> executable code are completely separated.  It makes no sense in
>>> Ada, where declarations are just as executable as statements.

>> I disagree. I think it does make sense because it clearly defines the scope
>> of the declared variable.
 
> Still, a somewhat *new* kind kind of handling exceptions in single
> declarations looks interesting?

> Given linear order of elaboration in declarative parts,
> and thus the possibility of sequencing initialization
> of local variables:
> 
>    procedure P is
>       declare
>          X1: constant T;  -- like Java final
>       begin
>          X1 := New_T(...);  -- may raise CE
>       exception
>          when Constraint_Error =>
>              X1 := Fallback_T;  -- better than Java final
>       end;
>       X2: D := New_D(X1, ...);  -- safely refer to X1
>    begin
>       ...
>    end P;

Huh, if you want closures, just say so. There is no need to break proven
language concepts in order to have desired effect:

procedure P is
    X1: constant T := -- Here anonymous function literal begins
       function return T is
       begin
            return New_T (...);  -- may raise CE
       exception
          when Constraint_Error =>
              return Fallback_T;  -- better than Java final
       end;
   X2: D := New_D (X1, ...);  -- safely refer to X1
begin
   ...
end P;

Note, no magic stuff, no exception handlers in declarations, just a simple
thing, which Ada should have had from the day one: functional types and
literals of.

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