Author: lwall
Date: 2009-10-09 00:55:49 +0200 (Fri, 09 Oct 2009)
New Revision: 28667
Modified:
docs/Perl6/Spec/S12-objects.pod
Log:
[S12] revise type subset pair notation a bit
Modified: docs/Perl6/Spec/S12-objects.pod
===================================================================
--- docs/Perl6/Spec/S12-objects.pod 2009-10-08 21:19:50 UTC (rev 28666)
+++ docs/Perl6/Spec/S12-objects.pod 2009-10-08 22:55:49 UTC (rev 28667)
@@ -13,8 +13,8 @@
Created: 27 Oct 2004
- Last Modified: 27 Sep 2009
- Version: 88
+ Last Modified: 8 Oct 2009
+ Version: 89
=head1 Overview
@@ -1494,22 +1494,23 @@
=head2 Abstract vs Concrete types [Conjectural]
-For any named type, certain other types may automatically be derived
+For any named type, certain other subset types may automatically be derived
from it by appending an appropriate adverbial to its name:
- Int:A Allow either defined or undefined Int values
+ Int:_ Allow either defined or undefined Int values
Int:U Allow only undefined (abstract) Int values
Int:D Allow only defined (concrete) Int values
That is, these are equivalent:
- Int:A Any where Int
- Int:U Int where !*.defined
- Int:D Int where *.defined
+ Int:U Int:_ where !*.defined
+ Int:D Int:_ where *.defined
A bare C<Int> may default differently in different circumstances.
-In a variable declaration, C<:A> is assumed, whereas in a formal
-parameter that is not an invocant, C<:D> is assumed.
+In variable declarations and in invocant declarations, C<:_> is
+assumed so that variables can convey undefinedness, whereas in a
+formal parameter that is not an invocant, C<:D> is assumed so that
+dispatch tends to fail to routines that are expecting defined values.
=head2 Multiple constraints
