Re: Optimizing Boundary Checks

[Vinzent Hoefler <ada.rocks@jlfencey.com>]

Robert I. Eachus wrote:

>Vinzent Hoefler wrote:
>
> > Yes, and finding this *very* useful, it reminds me, I would like to
> > have this feature for *every* variable, not just for arrays:
> >
> > As an example, currently
> >
> > |x : My_Enum;
> > |
> > |for i in x'Range loop ...
> >
> > doesn't work, you have to write
> >
> > |for in in My_Enum'Range loop
> >
> > each time. Is there any convincing explanation why it isn't allowed to
> > use the actual type of a variable instead of the type itself?
>
>No real reason, just no one saw the need for that particular attrbiute. 
>  You might want to post a request for the feature in Ada0Y to 
>Ada-Comment@ada-auth.org.

Perhaps I'll do. But then I would come up with a better justification
than just "it comes handy".

> > I can imagine situations (especially with subtypes) where it could be
> > handy to use the variables' type instead of an explicit type
> > specification.
>
>You will need a better justification than that!

Of course.

>But there is one. ;-)  A discrete variable declaration can have an 
>explict range in its subtype_indication:
>
>Size: Integer range 0 .. 1000;

Well, IMO that's bad style anyway.

>Of course, there is a real useful idiom which would need another 
>language change.  Right now the initial value, if it exists, is part of 
>the declaration of an object.  Again, no particular reason for that, but 
>RM8.3(14) would need to add another exception to its list.  It sure 
>would be nice though, to be able to say:
>
>Size: Integer range
>    Some_Expression..Some_Other_Complex_Expression := Size'First;

Well, as I said, anonymous types are bad style. The reason I would
like to have that feature is that sometimes I don't want to iterate
over the array of some Index_Type, instead I only want to initialize a
part of the array from a Sub_Index_Type. Currently I can write that by
specifying the type explicitely, but sometimes I change those types
and corresponding variables, so then the code breaks when I forget to
change the type specification in the loop.
And sometimes I even don't care about the actual variables type name
and just want to iterate over it's defined range whatever this
currently is.


Vinzent.

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