Author: larry
Date: Fri Sep 21 10:00:16 2007
New Revision: 14464
Modified:
doc/trunk/design/syn/S02.pod
doc/trunk/design/syn/S13.pod
Log:
Make easier way to specify outgoing coercions.
Typo from Thom++
Modified: doc/trunk/design/syn/S02.pod
==
--- doc/trunk/design/syn/S02.pod(original)
+++ doc/trunk/design/syn/S02.podFri Sep 21 10:00:16 2007
@@ -2171,7 +2171,7 @@
looks for the brackets. Despite not indicating a true subscript,
the brackets are similarly parsed as postfix operators. As postfixes
the brackets may be separated from their initial C<:foo> with either
-unspace or dot (or both), but nothgin else.
+unspace or dot (or both), but nothing else.
Regardless of syntax, adverbs used as named arguments generally show
up as optional named parameters to the function in question--even
Modified: doc/trunk/design/syn/S13.pod
==
--- doc/trunk/design/syn/S13.pod(original)
+++ doc/trunk/design/syn/S13.podFri Sep 21 10:00:16 2007
@@ -12,9 +12,9 @@
Maintainer: Larry Wall <[EMAIL PROTECTED]>
Date: 2 Nov 2004
- Last Modified: 2 Jun 2007
+ Last Modified: 21 Sep 2007
Number: 13
- Version: 9
+ Version: 10
=head1 Overview
@@ -141,6 +141,18 @@
on magical autogeneration. The default mappings correspond to the
standard fallback mappings of Perl 5 overloading.
+These deep mappings are mainly intended for infix operators that would have
+difficulty naming all their variants. Prefix operators tend to be simpler;
+note in particular that
+
+multi prefix:<~> is deep {...}
+
+is better written:
+
+method Str {...}
+
+(see below).
+
=head1 Type Casting
A class may define methods that allow it to respond as if it were a
@@ -189,9 +201,38 @@
it might call C, or it might pull a C with Spot's
identity from the dog cache, or it might do absolutely nothing if
C<$spot> already knows how to be a C. As a fallback, if no
-method responds to C<&.()>, the class will be asked to attempt to
+method responds to a coercion request, the class will be asked to attempt to
do C instead.
+It is also possible (and often preferable) to specify coercions from
+the other end, that is, for a class to specify how to coerce one of
+its values to some other class. If you define a method whose name
+is a declared type, it is taken as a coercion to that type:
+
+method Str { self.makestringval() }
+
+As with all methods, you can also export the corresponding multi:
+
+method Str is export { self.makestringval() }
+
+in which case you can use both calling forms:
+
+$x.Str
+Str($x)
+
+If the source class and the destination class both specify a
+coercion routine, the ambiguity is settled by the ordinary rules
+of multiple dispatch. Usually the source class will have the more
+specific argument and will win; ties are also possible, and those
+calls will fail. Additional arguments may sway the dispatch one way
+or the other depending on the candidate list.
+
+Note that, because the name of an anonymous class is unknown, coercion to
+an anonymous class can only be specified by the destination class:
+
+$someclass = generate_class();
+$someclass($x);
+
=cut
=for vim:set expandtab sw=4:
