Improve Element#attribute implementation as 6500x faster

benchmark/attribute.yaml

@@ -0,0 +1,38 @@
+loop_count: 1000
+contexts:
+  - gems:
+      rexml: 3.2.6
+    require: false
+    prelude: require 'rexml'
+  - name: master
+    prelude: |
+      $LOAD_PATH.unshift(File.expand_path("lib"))
+      require 'rexml'
+  - name: 3.2.6(YJIT)
+    gems:
+      rexml: 3.2.6
+    require: false
+    prelude: |
+      require 'rexml'
+      RubyVM::YJIT.enable
+  - name: master(YJIT)
+    prelude: |
+      $LOAD_PATH.unshift(File.expand_path("lib"))
+      require 'rexml'
+      RubyVM::YJIT.enable
+
+prelude: |
+  require 'rexml/document'
+
+  xml_source = "<deepest x:with_ns='foo' without_ns='bar'></deepest>"
+  100.times do
+    xml_source = "<nest>#{xml_source}</nest>"
+  end
+  xml_source = "<root xmlns:x='xyz'>#{xml_source}</root>"
+
+  document = REXML::Document.new(xml_source)
+  deepest_node = document.elements["//deepest"]
+
+benchmark:
+  with_ns:    deepest_node.attribute("with_ns", "xyz")
+  without_ns: deepest_node.attribute("without_ns")

lib/rexml/element.rb

@@ -1276,16 +1276,11 @@ def [](name_or_index)
     #   document.root.attribute("x", "a") # => a:x='a:x'
     #
     def attribute( name, namespace=nil )
-      prefix = nil
-      if namespaces.respond_to? :key
-        prefix = namespaces.key(namespace) if namespace
-      else
-        prefix = namespaces.index(namespace) if namespace
-      end
+      prefix = namespaces.key(namespace) if namespace
       prefix = nil if prefix == 'xmlns'
 
       ret_val =
-        attributes.get_attribute( "#{prefix ? prefix + ':' : ''}#{name}" )
+        attributes.get_attribute( prefix ? "#{prefix}:#{name}" : name )
 
       return ret_val unless ret_val.nil?
       return nil if prefix.nil?