Re: GNAT GPL 2013 bug?

[Adam Beneschan <adambeneschan@aol.com>]

On Monday, August 12, 2013 10:03:14 AM UTC-7, Dmitry A. Kazakov wrote:

> That implied null-exclusion for controlling parameters does not change/save
> anything. Just added language weirdness that
> 
>    "access T" is subtype conformant to "not null access T" depending on T
> 
> !, for apparently no gain.

Well, from the point of view of dynamic semantics, a call to a dispatching subprogram *has* to fail if given a null parameter.  There's no way around this.  So, dynamically, it's going to behave like a null-excluding access type no matter what.  From a static-semantics point of view, the language designers could have decreed that the parameter is *not* implicitly a null-excluding parameter even though it behaves like one at run-time.  That's a choice they could have made, although then someone else probably would have considered this to be "language weirdness".  They just can't win.

                               -- Adam