Re: Disallowing Pre-Defined Operations

["Tarjei Tj�stheim Jensen" <tarjei@online.no>]

Jean-Pierre Rosen wrote:

> Charles H. Sampson wrote:
> >      During the deliberations that led to Ada 95, was a mechanism for
> > disallowing the pre-defined operations of a type considered?  By "disal-
> > lowing" I mean some way of informing the compiler that an attempt to use
> > a certain pre-defined operation is a compile-time error.  Did anyone
> > even ask for it?  (Obviously I didn't, even though I've thought since
> > the mid-eighties that it would be a useful capability to have.)
>
> Not only was it considered - it's there.

[snip]

> function "/" (L, R : Length) return length is abstract;

That is really a workaround. I think both he and I would have preferred
something like

pragma disallow_predefined(operator => "/", a_type, a_type);
pragma disallow_predefined(operator => all, all, a_type);
pragma allow_predefined(operator => "+", a_type, a_type);
pragma map_predefined_result(result_type => integer, operator => "/", a_type,
a_type);

I think that would be more readable and a lot less work. It will of course not
work very well with a nonconforming compiler.

Greetings,