Re: access aliased obstacle

[dewar@cs.nyu.edu (Robert Dewar)]

tmoran says

"  I think of a C union as essentially a variant record with the
discriminant outside the record (in some other variable entirely).
C probably does think of this as a union, although it fits an Ada
discriminated record perfectly.  What is this 'Unchecked_Union'?
I don't see it in my LRM."

That is precisely the view that Unchecked_Union takes, it allows the
use of a variant record with no variant field stored, so it can exactly
map to a C union.

This pragma is implemented with consistent semantics in both the
Intermetrics compilers and in GNAT, and is used in the Win32 bindings.
For details, see the file features included with the GNAT documentation,
which has a full description of this pragma. You will definitely not
find it in the RM for the simple reason that it is not there. Tecnhnically
this is an imlementation defined attribute, but in practice it is one on
which there is agreement that it will be implemented consistently across
compilers.