Author: larry
Date: Wed Oct 1 09:55:35 2008
New Revision: 14583
Modified:
doc/trunk/design/syn/S03.pod
Log:
Describe how assignment metaoperators initialize undefined lvalues.
Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Wed Oct 1 09:55:35 2008
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 8 Mar 2004
- Last Modified: 10 Sep 2008
+ Last Modified: 1 Oct 2008
Number: 3
- Version: 139
+ Version: 140
=head1 Overview
@@ -3249,6 +3249,26 @@
($a,$b,$c) »+=» 1; # add one to each of three variables
+If you apply an assignment operator to a protoobject, it is assumed that
+you are implementing some kind of notional "reduction" to an accumulator
+variable. To that end, the base operator is dropped and a simple
+assignment is done instead. Hence you may correctly write:
+
+ my Num $prod;
+ for @factors -> $f {
+ $prod *= $f;
+ }
+
+While this may seem marginally useful in the scalar variable case,
+it's much more important for it to work this way when the modified
+location may have only just been created by autovivificatoin. In other
+words, if you write:
+
+ %prod{$key} *= $f
+
+you need not worry about whether the hash element exists yet. If it
+does not, it will simply be initialized with the value of C<$f>.
+
=head2 Negated relational operators
Any infix relational operator may be transformed into its negative
