Optimised performance for attribute extraction

.gitignore

@@ -15,3 +15,4 @@ spec/reports
 test/tmp
 test/version_tmp
 tmp
+*.swp

Rakefile

@@ -10,4 +10,9 @@ Rake::TestTask.new(:test) do |t|
   t.verbose = true
 end
 
+desc 'Benchmark'
+task :bench do
+  load 'bench/perf.rb' 
+end
+
 task :default => :test

bench/perf.rb

@@ -0,0 +1,43 @@
+require "rubygems"
+require "bundler/setup"
+require "active_model_serializers"
+require "active_support/json"
+require "benchmark"
+
+class User < Struct.new(:id,:name,:age,:about) 
+  include ActiveModel::SerializerSupport
+
+  def fast_hash
+    h = { 
+      id: read_attribute_for_serialization(:id), 
+      name: read_attribute_for_serialization(:name), 
+      about: read_attribute_for_serialization(:about)
+    }
+    h[:age] = read_attribute_for_serialization(:age) if age > 18
+    h
+  end
+end
+
+class UserSerializer < ActiveModel::Serializer
+  attributes :id, :name, :age, :about
+
+  def include_age?
+    object.age > 18
+  end
+end
+
+
+
+u = User.new(1, "sam", 10, "about")
+s = UserSerializer.new(u)
+
+n = 100000
+
+Benchmark.bmbm {|x| 
+  x.report("init") { n.times { UserSerializer.new(u) } }
+  x.report("fast_hash") { n.times { u.fast_hash } }
+  x.report("attributes") { n.times { UserSerializer.new(u).attributes } } 
+  x.report("serializable_hash") { n.times { UserSerializer.new(u).serializable_hash } }
+}   
+
+

lib/active_model/serializer.rb

@@ -93,6 +93,7 @@ def attribute(attr, options={})
         end
 
         define_include_method attr
+
       end
 
       def associate(klass, attrs) #:nodoc:
@@ -281,13 +282,9 @@ def as_json(options={})
     # object without the root.
     def serializable_hash
       return nil if @object.nil?
-      instrument(:serialize, :serializer => self.class.name) do
-        @node = attributes
-        instrument :associations do
-          include_associations! if _embed
-        end
-        @node
-      end
+      @node = attributes
+      include_associations! if _embed
+      @node
     end
 
     def include_associations!
@@ -378,13 +375,19 @@ def merge_association(hash, key, serializables, unique_values)
     # Returns a hash representation of the serializable
     # object attributes.
     def attributes
-      hash = {}
+      _fast_attributes
+      rescue NameError
+        method = "def _fast_attributes\n"
 
-      _attributes.each do |name,key|
-        hash[key] = read_attribute_for_serialization(name) if include?(name)
-      end
+        method << "  h = {}\n"
+
+        _attributes.each do |name,key|
+          method << "  h[:#{key}] = read_attribute_for_serialization(:#{name}) if send #{INCLUDE_METHODS[name].inspect}\n"
+        end
+        method << "  h\nend"
 
-      hash
+        self.class.class_eval method
+        _fast_attributes
     end
 
     # Returns options[:scope]