Re: have to use unrestricted access but just what about access

[Robert A Duff <bobduff@shell01.TheWorld.com>]

dewar@gnat.com (Robert Dewar) writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> wrote in message news:<wccznxqni7o.fsf@shell01.TheWorld.com>...
> > "chris.danx" <spamoff.danx@ntlworld.com> writes:
> > 
> > > How can the unrestricted_access attribute be replaced by just access in the
> > > following code?
> > 
> > You should be using 'Unchecked_Access here, which is a standard feature
> > of Ada (albeit unsafe).
> > 
> > 'Unrestricted_Access is a feature of GNAT, and is not necessary in your
> > example.
> > 
> > - Bob
> 
> Bob look again!

> One of the nasty restrictions in Ada 95 is that you cannot make parameters
> aliased. This means that they can never be used in access attributes. This
> is indeed one use of unrestricted access that is useful and legitimate, though
> of course passing such an access value out assumes call by reference, and you
> have to be sure that you can gaurantee call by reference.

Oh.  I thought we were talking about a *component* of a parameter, where
the component was explicitly declared aliased.  Also, you can make a
parameter aliased by making it tagged.

I agree that this is a nasty restriction in Ada 95 -- one ought to be
allowed to declare the parameter aliased explicitly, and taggedness
shouldn't have anything to do with the matter.

- Bob