Author: lwall
Date: 2009-09-01 01:42:06 +0200 (Tue, 01 Sep 2009)
New Revision: 28150
Modified:
docs/Perl6/Spec/S03-operators.pod
Log:
[S03] steal ::= for readonly binding ala sigs
Modified: docs/Perl6/Spec/S03-operators.pod
===================================================================
--- docs/Perl6/Spec/S03-operators.pod 2009-08-31 21:06:36 UTC (rev 28149)
+++ docs/Perl6/Spec/S03-operators.pod 2009-08-31 23:42:06 UTC (rev 28150)
@@ -14,8 +14,8 @@
Created: 8 Mar 2004
- Last Modified: 29 Aug 2009
- Version: 170
+ Last Modified: 31 Aug 2009
+ Version: 171
=head1 Overview
@@ -1465,14 +1465,28 @@
=item *
-C<< infix:<::=> >>, compile-time binding
+C<< infix:<::=> >>, bind and make readonly
$signature ::= $capture
-This does the same as C<:=> except it does it at compile time. (This implies
-that the expression on the right is also evaluated at compile time; it does
-not bind a lazy thunk.)
+This does the same as C<:=>, then marks any destination parameters as
+readonly (unless the individual parameter overrides this with either
+the C<rw> trait or the C<copy> trait). It's particularly useful
+for establishing readonly context variables for a dynamic scope:
+ {
+ my $*OUT ::= open($file, :w) || die $!;
+ doit(); # runs with redirected stdout
+ }
+ doit(); # runs with original stdout
+
+If C<doit> wants to change C<$*OUT>, it must declare its own
+contextual variable. It may not simply assign to C<$*OUT>.
+
+Note that the semantics of C<::=> are virtually identical to
+the normal binding of arguments to formal subroutine parameters
+(which also default to readonly).
+
=item *
C<< infix:{'=>'} >>, Pair constructor
