Re: Two ideas for the next Ada Standard

[ok@goanna.cs.rmit.edu.au (Richard A. O'Keefe)]

dewar@cs.nyu.edu (Robert Dewar) writes:

>Richard, you can't quite do 100% of what you want, since you cannot exclude
>attributes like Image, but you are obviously missing an important capability
>in Aa 95.

>	type x is range 1..10;
>        function "+" (a,b : x) return x is abstract;

>causes the addition operator to be unavailable for this type.
>This is how weakening is done in Ada 95.

I had actually seen this in a thread earlier this year.  (comp.lang.ada
_is_ such good value.)  However, 'Image is one of the things that would
merit suppression:  it would be nice to export an enumeration type _as_
an enumeration type without having to provide all the names as strings.

So far the only way I've been able to figure out of exporting some
of the enumeration literals of an enumeration type is

	package foo is
	    type T is private;
	    function X return T;
	    function Z return T;
	private
	    type T is (X, Y, Z, W);
	end foo;

At least, I _thought_ it should work.  Enumeration literals are
parameterless functions returning values of the type, not so?
But gnat says that the declarations of X and Z in the private
part _conflict_ with the earlier declarations (instead of, as I
thought, matching them), and who am I to argue?

My reaction to this was not to look through the standard for the fine
print explaining why I can't do it this way, but to stop trying.
Exporting half an enumeration type is probably too silly.

-- 
Australian citizen since 14 August 1996.  *Now* I can vote the xxxs out!
Richard A. O'Keefe; http://www.cs.rmit.edu.au/%7Eok; RMIT Comp.Sci.