Author: larry Date: Mon Sep 18 20:33:07 2006 New Revision: 12185 Modified: doc/trunk/design/syn/S02.pod
Log: Some handwaving about type equivalence. Modified: doc/trunk/design/syn/S02.pod ============================================================================== --- doc/trunk/design/syn/S02.pod (original) +++ doc/trunk/design/syn/S02.pod Mon Sep 18 20:33:07 2006 @@ -12,9 +12,9 @@ Maintainer: Larry Wall <[EMAIL PROTECTED]> Date: 10 Aug 2004 - Last Modified: 13 Sept 2006 + Last Modified: 18 Sept 2006 Number: 2 - Version: 68 + Version: 69 This document summarizes Apocalypse 2, which covers small-scale lexical items and typological issues. (These Synopses also contain @@ -346,6 +346,25 @@ =item * +Types are officially compared using name equivalence rather than +structural equivalence. However, we're rather liberal in what we +consider a name. For example, the name includes the version and +authority associated with the module defining the type (even if +the type itself is "anonymous"). Beyond that, when you instantiate +a parametric type, the arguments are considered part of the "long +name" of the resulting type, so one C<Array of Int> is equivalent to +another C<Array of Int>. (Another way to look at it is that the type +instantiation "factory" is memoized.) Typename aliases are considered +equivalent to the original type. + +This name equivalence of parametric types extends only to parameters +that can be considered immutable (or that at least can have an +immutable snapshot taken of them). Two distinct classes are never +considered equivalent even if they have the same attributes because +classes are not considered immutable. + +=item * + Perl 6 supports the notion of B<properties> on various kinds of objects. Properties are like object attributes, except that they're managed by the individual object rather than by the object's class.
