Proper namespace support for attributes.

This separates namespace handling into namespace names and namespace objects.
The namespace objects are retrieved from the element an attribute belongs to.
Once retrieved the namespace is cached, due to the overhead of retrieving
namespaces in large documents.

lib/oga/xml/attribute.rb

@@ -7,35 +7,44 @@ module Oga
     #  The name of the attribute.
     #  @return [String]
     #
-    # @!attribute [rw] namespace
-    #  The namespace of the attribute.
-    #  @return [Oga::XML::Namespace]
+    # @!attribute [rw] namespace_name
+    #  @return [String]
     #
     # @!attribute [rw] value
     #  The value of the attribute.
     #  @return [String]
     #
+    # @!attribute [r] element
+    #  The element this attribute belongs to.
+    #  @return [Oga::XML::Element]
+    #
     class Attribute
-      attr_accessor :name, :namespace, :value
+      attr_accessor :name, :namespace_name, :element, :value
 
       ##
       # @param [Hash] options
       #
       # @option options [String] :name
-      # @option options [Oga::XML::Namespace] :namespace
+      # @option options [String] :namespace_name
       # @option options [String] :value
+      # @option options [Oga::XML::Element] :element
       #
       def initialize(options = {})
-        if options[:namespace] and !options[:namespace].is_a?(Namespace)
-          raise(
-            TypeError,
-            ':namespace must be an instance of Oga::XML::Namespace'
-          )
-        end
+        @name    = options[:name]
+        @value   = options[:value]
+        @element = options[:element]
 
-        @name      = options[:name]
-        @namespace = options[:namespace]
-        @value     = options[:value]
+        @namespace_name = options[:namespace_name]
+      end
+
+      ##
+      # Returns the {Oga::XML::Namespace} instance for the current namespace
+      # name.
+      #
+      # @return [Oga::XML::Namespace]
+      #
+      def namespace
+        return @namespace ||= element.available_namespaces[namespace_name]
       end
 
       ##

lib/oga/xml/namespace.rb

@@ -4,16 +4,24 @@ module Oga
     # The Namespace class contains information about XML namespaces such as the
     # name and URI.
     #
+    # @!attribute [r] name
+    #  @return [String]
+    #
+    # @!attribute [r] uri
+    #  @return [String]
+    #
     class Namespace
-      attr_accessor :name
+      attr_accessor :name, :uri
 
       ##
       # @param [Hash] options
       #
       # @option options [String] :name
+      # @option options [String] :uri
       #
       def initialize(options = {})
         @name = options[:name]
+        @uri  = options[:uri]
       end
 
       ##
@@ -27,7 +35,7 @@ module Oga
       # @return [String]
       #
       def inspect
-        return "Namespace(name: #{name.inspect})"
+        return "Namespace(name: #{name.inspect} uri: #{uri.inspect})"
       end
     end # Namespace
   end # XML

lib/oga/xml/parser.y

@@ -150,9 +150,7 @@ rule
     # foo:bar
     | T_ATTR_NS T_ATTR
       {
-        ns = Namespace.new(:name => val[0])
-
-        Attribute.new(:namespace => ns, :name => val[1])
+        Attribute.new(:namespace_name => val[0], :name => val[1])
       }
     ;