X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FMoose%2FManual%2FRoles.pod;h=9ad655668b2ab9a52f1f59cc680a1337b4698ad1;hb=f9b1ab71234d11a9121de96c574ca980bbfb3eaa;hp=3e7397fff3640a19a43f9f43fd31e442ea7d01a4;hpb=2840a3b25fac3ab606e2053ce9ef30b39687270d;p=gitmo%2FMoose.git

diff --git a/lib/Moose/Manual/Roles.pod b/lib/Moose/Manual/Roles.pod
index 3e7397f..9ad6556 100644
--- a/lib/Moose/Manual/Roles.pod
+++ b/lib/Moose/Manual/Roles.pod
@@ -2,20 +2,22 @@
 
 =head1 NAME
 
-Moose::Manual::Roles - Roles, an Alternative to Deep Hierarchies and Base Classes
+Moose::Manual::Roles - Roles, an alternative to deep hierarchies and base classes
 
 =head1 WHAT IS A ROLE?
 
 A role is something that classes do. Usually, a role encapsulates some
 piece of behavior or state that can be shared between classes. It is
-important to understand that I<roles are not classes>. Roles do not
-participate in inheritance, and a role cannot be instantiated.
+important to understand that I<roles are not classes>. You cannot
+inherit from a role, and a role cannot be instantiated. We sometimes
+say that roles are I<consumed>, either by classes or other roles.
 
 Instead, a role is I<composed> into a class. In practical terms, this
 means that all of the methods and attributes defined in a role are
-added directly to (we sometimes say ("flattened into") the class that
-consumes the role. These attributes and methods then show up in the
-class as if they were defined directly in the class.
+added directly to (we sometimes say "flattened into") the class that
+consumes the role. These attributes and methods then appear as if they
+were defined in the class itself. A subclass of the consuming class
+will inherit all of these methods and attributes.
 
 Moose roles are similar to mixins or interfaces in other languages.
 
@@ -46,7 +48,7 @@ Creating a role looks a lot like creating a Moose class:
       $self->is_broken(1);
   }
 
-Except for our use of C<Moose::Role>, this looks just like a class
+Except for our use of L<Moose::Role>, this looks just like a class
 definition with Moose. However, this is not a class, and it cannot be
 instantiated.
 
@@ -122,18 +124,14 @@ methods:
 If we try to consume this role in a class that does not have a
 C<break> method, we will get an exception.
 
-Note that attribute-generated accessors do not satisfy the requirement
-that the named method exists. Similarly, a method modifier does not
-satisfy this requirement either. This may change in the future.
-
-You can also see that we added a method modifier on
-C<break>. Basically, we want consuming classes to implement their own
-logic for breaking, but we make sure that the C<is_broken> attribute
-is always set to true when C<break> is called.
+You can see that we added a method modifier on C<break>. We want
+classes that consume this role to implement their own logic for
+breaking, but we make sure that the C<is_broken> attribute is always
+set to true when C<break> is called.
 
   package Car
 
-      use Moose;
+  use Moose;
 
   with 'Breakable';
 
@@ -150,6 +148,24 @@ is always set to true when C<break> is called.
       }
   }
 
+=head2 Roles Versus Abstract Base Classes
+
+If you are familiar with the concept of abstract base classes in other
+languages, you may be tempted to use roles in the same way.
+
+You I<can> define a "interface-only" role, one that contains I<just> a
+list of required methods.
+
+However, any class which consumes this role must implement all of the
+required methods, either directly or through inheritance from a
+parent. You cannot delay the method requirement check so that they can
+be implemented by future subclasses.
+
+Because the role defines the required methods directly, adding a base
+class to the mix would not achieve anything. We recommend that you
+simply consume the interface role in each class which implements that
+interface.
+
 =head1 USING METHOD MODIFIERS
 
 Method modifiers and roles are a very powerful combination.  Often, a
@@ -180,7 +196,7 @@ If a class composes multiple roles, and those roles have methods of
 the same name, we will have a conflict. In that case, the composing
 class is required to provide its I<own> method of the same name.
 
-  package Breakdances;
+  package Breakdancer;
 
   use Moose::Role
 
@@ -234,6 +250,21 @@ C<Breakable> and C<BreakDancer>, but does not provide a C<break>
 method. If some API expects an object that does one of those roles, it
 probably expects it to implement that method.
 
+In some use cases we might alias and exclude methods from roles, but
+then provide a method of the same name in the class itself.
+
+=head1 ROLE EXCLUSION
+
+A role can say that it cannot be combined with some other role. This
+should be used with great caution, since it limits the re-usability of
+the role.
+
+  package Breakable;
+
+  use Moose::Role;
+
+  excludes 'BreakDancer';
+
 =head1 AUTHOR
 
 Dave Rolsky E<lt>autarch@urth.orgE<gt>