Re: Half Constrained Array Types and Slices

[brian.b.mcguinness@lmco.com]

Jeff Carter wrote:
> I've been thinking about a language that allows null arrays, even for
> degenerate types like
>
> type Single is (One);
>
> type Degenerate is array (Single range <>) of Whatever;
>
> Suppose we could say something like
>
> V : Degenerate (null range); -- V'Length = 0
>
> Now we can do things like
>
> for I in V'range loop -- loop is not entered
>
> if X in V'range -- always False
>
> Y : Degenerate (V'range); -- Y'Length = 0
>
> More importantly, we do these kinds of things in subprograms with
> Degenerate parameters.
>
> If Degenerate is a string type, "" is meaningful.
>
> We seem to be fine as long as we don't do V'Last. I can't figure out
> how such a language should handle 'First and 'Last for such a
> value/object. Probably a failure of imagination on my part.

Perhaps I misunderstand you, but hasn't this capability already been
provided in the 
Vector container?

--- Brian