Re: Array Help?

[stefan-lucks@see-the.signature]

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. 

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
    -- inside Sort, Items'First=1 and Item'Last = Items'Length
    -- regardless of the index type of the actual parameter
  begin
     ...
  end Sort;

and later call the same Sort procedure

  Sort(X);
  Sort(Y);
  Sort(Z);

for any one-dimensional array of type T, e.g.,  

  X: array (Positive range 3 .. 13) of T;
  Y: array (range 31 .. 3343) of T;
  type Month_Names is (January, [...] December);
  Z: array (Month_Names) of T;



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