Author: larry Date: Fri Mar 9 16:38:18 2007 New Revision: 14325 Modified: doc/trunk/design/syn/S11.pod
Log: As noted by allbery_b++, Smylers++, and david.green++, we've thoroughly neglected to thoroughly spec the intended version sharing and emulation model. Modified: doc/trunk/design/syn/S11.pod ============================================================================== --- doc/trunk/design/syn/S11.pod (original) +++ doc/trunk/design/syn/S11.pod Fri Mar 9 16:38:18 2007 @@ -12,9 +12,9 @@ Maintainer: Larry Wall <[EMAIL PROTECTED]> Date: 27 Oct 2004 - Last Modified: 8 Mar 2006 + Last Modified: 9 Mar 2006 Number: 11 - Version: 16 + Version: 17 =head1 Overview @@ -351,6 +351,41 @@ specifically rules out any prereleases. +If two different modules in your program require two different +versions of the same module, Perl will simply load both versions at +the same time. For modules that do not manage exclusive resources, +the only penalty for this is memory, and the disk space in the library +to hold both the old and new versions. For modules that do manage +an exclusive resource, such as a database handle, there are two approaches +short of requiring the user to upgrade. The first is simply to refactor +the module into a stable supplier of the exclusive resource that doesn't +change version often, and then the outer wrappers of that resource can +both be loaded and use the same supplier of the resource. + +The other approach is for the module to keep the management of its exclusive +resource, but offer to emulate older versions of the API. Then if there +is a conflict over which version to use, the new one is used by both users, +but each gets a view that is consistent with the version it thinks it is +using. Of course, this depends crucially on how well the new version +actually emulates the old version. + +To declare that a module emulates an older version, declare it like this: + + class Dog:<1.2.1 cpan:JRANDOM> emulates :<1.2.0>; + +Or to simply exclude use of the older module and (presumably) force +the user to upgrade: + + class Dog:<1.2.1 cpan:JRANDOM> excludes :<1.2.0>; + +The name is parsed like a C<use> wildcard, and you can have more than one, +so you can say things like: + + class Dog:<1.2.1 cpan:JRANDOM> + emulates Dog:auth(DCONWAY|JCONWAY|TCONWAY):ver<1.0+> + excludes Fox:<3.14159 http://oreillymedia.com> + emulates Wolf:from<C# 0.8..^1.0>; + =head1 Forcing Perl 6 To get Perl 6 parsing rather than the default Perl 5 parsing,
