Don't define a coercion directly to a class like URI. Make a subtype

and coerce that instead.

diff --git a/lib/Moose/Cookbook/Basics/Recipe5.pod b/lib/Moose/Cookbook/Basics/Recipe5.pod
index 2f0208d..a16f60d 100644 (file)
--- a/lib/Moose/Cookbook/Basics/Recipe5.pod
+++ b/lib/Moose/Cookbook/Basics/Recipe5.pod
@@ -15,17 +15,17 @@ Moose::Cookbook::Basics::Recipe5 - More subtypes, coercion in a B<Request> class
   use Params::Coerce ();
   use URI            ();
 
-  class_type('HTTP::Headers');
+  subtype 'My.HTTP::Headers' => as class_type('HTTP::Headers');
 
-  coerce 'HTTP::Headers'
+  coerce 'My.HTTP::Headers'
       => from 'ArrayRef'
           => via { HTTP::Headers->new( @{$_} ) }
       => from 'HashRef'
           => via { HTTP::Headers->new( %{$_} ) };
 
-  class_type('URI');
+  subtype 'My.URI' => as class_type('HTTP::Headers');
 
-  coerce 'URI'
+  coerce 'My.URI'
       => from 'Object'
           => via { $_->isa('URI')
                    ? $_
@@ -37,13 +37,13 @@ Moose::Cookbook::Basics::Recipe5 - More subtypes, coercion in a B<Request> class
       => as 'Str'
       => where { /^HTTP\/[0-9]\.[0-9]$/ };
 
-  has 'base' => ( is => 'rw', isa => 'URI', coerce => 1 );
-  has 'uri'  => ( is => 'rw', isa => 'URI', coerce => 1 );
+  has 'base' => ( is => 'rw', isa => 'My.URI', coerce => 1 );
+  has 'uri'  => ( is => 'rw', isa => 'My.URI', coerce => 1 );
   has 'method'   => ( is => 'rw', isa => 'Str' );
   has 'protocol' => ( is => 'rw', isa => 'Protocol' );
   has 'headers'  => (
       is      => 'rw',
-      isa     => 'HTTP::Headers',
+      isa     => 'My.HTTP::Headers',
       coerce  => 1,
       default => sub { HTTP::Headers->new }
   );
@@ -61,10 +61,16 @@ set the C<coerce> attribute parameter to a true value.
 
 First, we create the subtype to which we will coerce the other types:
 
-  class_type('HTTP::Headers');
+  subtype 'My.HTTP::Headers' => as class_type('HTTP::Headers');
+
+We are creating a subtype rather than using C<HTTP::Headers> as a type
+directly. The reason we do this is coercions are global, and a
+coercion defined for C<HTTP::Headers> in our C<Request> class would
+then be defined for I<all> Moose-using classes in the current Perl
+interpreter. It's a L<best practice|Moose::Manual::BestPractices> to
+avoid this sort of namespace pollution.
 
-The C<class_type> sugar function is simply a shortcut for something
-like this:
+The C<class_type> sugar function is simply a shortcut for this:
 
   subtype 'HTTP::Headers'
       => as 'Object'
@@ -92,7 +98,7 @@ to accept those data structure instead of an B<HTTP::Headers>
 instance, and just do the right thing. This is exactly what coercion
 is for:
 
-  coerce 'HTTP::Headers'
+  coerce 'My.HTTP::Headers'
       => from 'ArrayRef'
           => via { HTTP::Headers->new( @{$_} ) }
       => from 'HashRef'
@@ -108,7 +114,7 @@ we want a particular attribute to be coerced:
 
   has 'headers' => (
       is      => 'rw',
-      isa     => 'Header',
+      isa     => 'My.HTTP::Headers',
       coerce  => 1,
       default => sub { HTTP::Headers->new }
   );
@@ -131,11 +137,11 @@ help implement coercions. In this case we use L<Params::Coerce>.
 Once again, we need to declare a class type for our non-Moose L<URI>
 class:
 
-  class_type('URI');
+  subtype 'My.URI' => as class_type('HTTP::Headers');
 
 Then we define the coercion:
 
-  coerce 'URI'
+  coerce 'My.URI'
       => from 'Object'
           => via { $_->isa('URI')
                    ? $_
@@ -158,8 +164,8 @@ string is assumed to be an C<http> URI.
 
 Finally, we need to make sure our attributes enable coercion.
 
-  has 'base' => ( is => 'rw', isa => 'URI', coerce => 1 );
-  has 'uri'  => ( is => 'rw', isa => 'URI', coerce => 1 );
+  has 'base' => ( is => 'rw', isa => 'My.URI', coerce => 1 );
+  has 'uri'  => ( is => 'rw', isa => 'My.URI', coerce => 1 );
 
 Re-using the coercion lets us enforce a consistent API across multiple
 attributes.

diff --git a/t/000_recipes/basics/005_coercion.t b/t/000_recipes/basics/005_coercion.t
index d45cf69..224c084 100644 (file)
--- a/t/000_recipes/basics/005_coercion.t
+++ b/t/000_recipes/basics/005_coercion.t
@@ -22,17 +22,17 @@ use Test::Exception;
     use Params::Coerce ();
     use URI            ();
 
-    class_type('HTTP::Headers');
+    subtype 'My.HTTP::Headers' => as class_type('HTTP::Headers');
 
-    coerce 'HTTP::Headers'
+    coerce 'My.HTTP::Headers'
         => from 'ArrayRef'
             => via { HTTP::Headers->new( @{$_} ) }
         => from 'HashRef'
             => via { HTTP::Headers->new( %{$_} ) };
 
-    class_type('URI');
+    subtype 'My.URI' => as class_type('HTTP::Headers');
 
-    coerce 'URI'
+    coerce 'My.URI'
         => from 'Object'
             => via { $_->isa('URI')
                      ? $_
@@ -44,13 +44,13 @@ use Test::Exception;
         => as 'Str'
         => where { /^HTTP\/[0-9]\.[0-9]$/ };
 
-    has 'base' => ( is => 'rw', isa => 'URI', coerce => 1 );
-    has 'uri'  => ( is => 'rw', isa => 'URI', coerce => 1 );
+    has 'base' => ( is => 'rw', isa => 'My.URI', coerce => 1 );
+    has 'uri'  => ( is => 'rw', isa => 'My.URI', coerce => 1 );
     has 'method'   => ( is => 'rw', isa => 'Str' );
     has 'protocol' => ( is => 'rw', isa => 'Protocol' );
     has 'headers'  => (
         is      => 'rw',
-        isa     => 'HTTP::Headers',
+        isa     => 'My.HTTP::Headers',
         coerce  => 1,
         default => sub { HTTP::Headers->new }
     );