Author: larry
Date: Wed Dec 20 18:42:50 2006
New Revision: 13497
Modified:
doc/trunk/design/syn/S03.pod
Log:
Made Range objects smarter about transforms.
Modified: doc/trunk/design/syn/S03.pod
==============================================================================
--- doc/trunk/design/syn/S03.pod (original)
+++ doc/trunk/design/syn/S03.pod Wed Dec 20 18:42:50 2006
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 8 Mar 2004
- Last Modified: 5 Dec 2006
+ Last Modified: 20 Dec 2006
Number: 3
- Version: 77
+ Version: 78
=head1 Changes to Perl 5 operators
@@ -535,6 +535,35 @@
so C<^Moose> is short for C<HOW(Moose)> or C<Moose.HOW>. It still kinda
means "what is this thing's domain" in an abstract sort of way.
+=item * Since use of C<Range> objects in scalar context is usually
+non-sensical, a C<Range> object used as an operand for scalar operators
+will generally attempt to distribute the operator to its endpoints and
+return another suitably modified C<Range> instead. (Notable exceptions
+include C<< infix:<~~> >>, which does smart matching, and C<< prefix:<+> >>
+which returns the length of the range.) Therefore if you wish to
+write a slice using a length instead of an endpoint, you can say
+
+ @foo[ start() + ^$len ]
+
+which is short for:
+
+ @foo[ start() + (0..^$len) ]
+
+which is equivalent to something like:
+
+ @foo[ list do { my $tmp = start(); $tmp ..^ $tmp+$len } ]
+
+In other words, operators of numeric and other ordered types are
+generally overloaded to do something sensible on C<Range> objects.
+In particular, multiplicative operators not only multiply the endpoints
+but also the "by" of the C<Range> object:
+
+ (1..11:by(2)) * 5 # same as 5..55:by(10)
+ 5,15,25,35,45,45,55
+
+Conjecture: non-linear functions might even produce non-uniform "by" values!
+Think of log scaling, for instance.
+
=item * The C<...> operator is the "yada, yada, yada" list operator,
which is used as the body in function prototypes. It complains
bitterly (by calling C<fail>) if it is ever executed. Variant C<???>
