Re: Converting C++ class to Ada

[Stephen Leake <Stephen.Leake@gsfc.nasa.gov>]

Robert A Duff wrote:
> 
> In article <JSA.96Dec18184555@alexandria>,
> Jon S Anthony <jsa@alexandria> wrote:
> >> Also, if I wanted to make sure that "null" wasn't used as one of the
> >> discriminants, would I have to use "access Motor.Object_Type" rather
> >> than the declared access type?
> >
> >Neither will prevent that.
> 
> A value of an anonymous access type can never be null.  (This includes
> both access parameters and access discriminants.)  Run-time checks
> ensure this.
> 
> - Bob

I can't find a rule in the RM that says this. In "Ada as a Second
Language", page 491, Norman Cohen says "Elaboration of a discriminant
constraint raises the exception Constriant_Error if the value given for
an access disciminant is null". So I believe an access discriminant
cannot be null, but I'm trying to hone my RM reading skills. Searching
for "access discriminant" gave no rule regarding null values. As Jon
Anthony pointed out, 11.5, which lists ALL defined checks, does not
mention checking access discriminants for null, only access parameters.
So where is the rule?
-- 
- Stephe