Author: diakopter
Date: 2010-05-20 01:41:19 +0200 (Thu, 20 May 2010)
New Revision: 30721
Modified:
docs/Perl6/Spec/S06-routines.pod
Log:
[S06] specify syntax for strongly-typed closure variables
Modified: docs/Perl6/Spec/S06-routines.pod
===================================================================
--- docs/Perl6/Spec/S06-routines.pod 2010-05-19 19:11:39 UTC (rev 30720)
+++ docs/Perl6/Spec/S06-routines.pod 2010-05-19 23:41:19 UTC (rev 30721)
@@ -192,6 +192,27 @@
anon RETTYPE sub ( PARAMS ) TRAITS {...}
+When an anonymous subroutine will be assigned to a scalar variable,
+the variable can be declared with the signature of the routines that
+will be assigned to it:
+
+ my &:(Str, int, int --> Grammar) $grammar_factory;
+ $grammar_factory = sub (Str $name, int $n, int $x --> Grammar) { ... };
+
+Covariance allows a routine (that has a more derived return type than what is
+defined in the scalar's signature) to be assigned to that scalar.
+Contravariance allows a routine (with parameter types that are less derived
+than those in the scalar's signature) to be assigned to that scalar. The
+compiler may choose to enforce (by type-checking) such assignments at
+compile-time, if possible. Such type annotations are intended to help the
+compiler optimize code to the extent such annotations are included and/or to
+the extent they aid in type inference.
+
+The same signature can be used to mark the type of a closure parameter to
+another subroutine:
+
+ sub (int $n, &:(Str, int, int --> Grammar) --> Str) { ... }
+
B<Trait> is the name for a compile-time (C<is>) property.
See L<"Properties and traits">.
