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Dmitry A. Kazakov a écrit :
> 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@[EMAIL PROTECTED]
> 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.
You can do that but not in an anonymous way, so what's the point? I
think it not a good practive to use anonymous function or procedure, it
makes hard to read code (and it's one of the feature of ada: easy to read)
I prefer this kind of writing:
procedure P is
function Init_T return T;
function Init_T return T is
begin
return New_T (...); -- may raise CE
exception
when Constraint_Error =>
return Fallback_T; -- better than Java final
end;
X1: constant T := Init_T; -- Here anonymous function literal begins
X2: D := New_D (X1, ...); -- safely refer to X1
begin
...
end P;
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