CVS difference for ais/ai-00231.txt

Differences between 1.4 and version 1.5
Log of other versions for file ais/ai-00231.txt

--- ais/ai-00231.txt	2003/01/24 04:14:27	1.4
+++ ais/ai-00231.txt	2003/06/07 04:58:55	1.5
@@ -173,3 +173,60 @@
    not_constraint ::= NOT Friday
 
 *************************************************************
+
+From: Tucker Taft
+Sent: Tuesday, May 6, 2003  2:49 PM
+
+During the AdaUK Ada 200Y workshop, Franco Gasperoni made a good
+suggestion.  He felt it will be too confusing to make "access T" mean "access
+all T not null" (I think others have made this point as well).
+
+Why not just change the semantics of "access T" to allow null (though
+when used as a controlling operand, there will be a run-time
+check for non-null), so that "access all T" and "access T" are
+synonyms.  This will be upward compatible for programs that
+don't raise Constraint_Error, and the slight potential
+performance degradation when the non-null aspect of access T was
+important can be made up for by using "not null" explicitly.
+
+This seems like a reasonable suggestion, and is probably one
+we have debated in the past, and just were perhaps worried
+about the compatibility issue.  But in fact, I suspect this
+is the kind of thing that may fix more bugs that it creates.
+Most uses of anon access types are for controlling operands,
+and those will see no change.  The other uses often discover
+a need to pass "null" eventually, and then have to switch
+to a named access type, or play some other game.
+
+Certainly when interfacing with C or Java, an "access T" that allows
+null will be more useful.  And altough we could say that
+"access T" is just a convenient shorthand for "access all T not null"
+it does seem like a recipe for confusion when teaching Ada 200Y.
+
+It seems like if the non-null aspect of an access parameter is
+important, users will welcome the chance to say "not null" explicitly.
+
+*************************************************************
+
+From: John Barnes
+Sent: Thursday, May 8, 2003  1:28 AM
+
+Good idea..  I always hated the potential confusion as it was.
+
+*************************************************************
+
+From: Gary Dismukes
+Sent: Tuesday, May 13, 2003  6:33 AM
+
+I agree that this seems like a sensible change with minimal disadvantages.
+
+*************************************************************
+
+From: Robert A Duff
+Sent: Thursday, May 8, 2003  7:34 AM
+
+Me, three.
+
+*************************************************************
+
+*************************************************************

Questions? Ask the ACAA Technical Agent