Re: Array Help?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

stefan-lucks@see-the.signature writes:

> On Wed, 29 Feb 2012, Robert A Duff wrote:
>
>> Anyway, slices aren't really all that useful -- for many array types,
>> you don't need them at all.  And slices as l-values, as in your
>> example, are quite rare, because you really want to be able to
>> change the length of the slice, if you want to change it at all.
>
> Not quite. I quite frequently use something like
>
>   X := X(X'Last) & (X'First .. X'Last-1) 
>
> and 
>
>   First := X'First; 
>   while First < X'Last and then X(First) = ' ' loop 
>     First := First + 1;
>   end loop; 
>   return X(First .. X'Last);
>
> and similar constructs, where array slicing is a highly useful language 
> feature. 

Mildly useful, I'd say.  If you didn't have slices, you'd have to
write a few lines of code instead of the above -- an extra loop.
That's a purely local change.  No big deal.

Contrast that with features like packages, private types, user-defined
integer types, etc, the lack of which would damage the entire structure
of your program.

Sure, slices are useful, and I use them.  But I wouldn't mind too
much if they didn't exist.  It's trivial to write a Slice function
that does what "A(F..L)" does.

You didn't address my point about l-values.  None of your slices
above are l-values.  L-value slices cause a lot of implementation
trouble, and are nearly useless -- the language would be better
off without them.

> On the other hand, I agree that the fact that array slices carry their 
> original indices with them is a misfeature of Ada. 
>
> I would appreciate way to convert ingoing parameters into some standard 
> indexing. For example (inventing a new syntax variant on the fly):
>
>   procedure Sort(Items: in out array(generic Positive range <>) of T) is

Interesting idea.

- Bob