Re: A Bug in VAX Ada (ACCVIO)

[ASP@SEI.CMU.EDU (Spencer Peterson)]

This message is a response to the perceived bug found with VAX Ada using
an access type, UNCHECKED_DEALLOCATION and a constant and a variable of 
the access type. "Ceci est un exemple..."

The "exemple" procedure/program is ERRONEOUS.  I quote, with meaningful 
substitutions, from the Ada Reference Manual( Chapter 13.10.1, Para. 6).

"If A and B designate the same object, then accessing that object through 
B is erroneous if this access is performed (or attempted) after the call 
DISPOSE(A); the effect of each such access is not defined by the language."

The program behaves as correctly as it can, given that it is 'legal' for
a compiler to optimize use of storage by NOT allocating a fresh copy of 
the string contents, although it would be prefered that a second copy be
made and thus, no problem would occur when the original is DISPOSEd. The
effect of making a copy of the contents of an access type, in this case,
is the same as if B were a constant of type ACCESS_STRING, i.e.
   B : constant ACCESS_STRING := A;

Spencer Peterson
Member of The Technical Staff
Software Engineering Institute
Carnegie Mellon University
5000 Forbes Ave.
Pittsburgh, PA 15213
412-268-7608