CVS difference for ais/ai-00231.txt

Differences between 1.3 and version 1.4
Log of other versions for file ais/ai-00231.txt

--- ais/ai-00231.txt	2002/10/01 03:08:53	1.3
+++ ais/ai-00231.txt	2003/01/24 04:14:27	1.4
@@ -147,3 +147,29 @@
 an access-to-constant type.
 
 *************************************************************
+
+From: Dan Eilers
+Sent: Friday, January 17, 2003  2:41 PM
+
+AI-231 proposes the syntax:
+
+    not_null_constraint ::= NOT NULL
+
+for null-excluding subtypes of a named access type.
+
+I propose generalizing this to allow value-excluding subtypes
+of other named types, serving the same purpose:
+
+> The general ability to specify an access subtype that excludes null for both
+> named and anonymous access types can provide useful documentation and higher
+> efficiency. This is especially true for parameters, by allowing the nullness
+> check to be "pushed" to the caller, where it can be more likely removed.
+
+The same principle applies to the division-by-zero check.
+
+   not_constraint ::= NOT NULL
+   not_constraint ::= NOT 0
+   not_constraint ::= NOT 0.0
+   not_constraint ::= NOT Friday
+
+*************************************************************

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