Make json.extract! accept objects with internal hash implementation

lib/jbuilder.rb

@@ -213,10 +213,8 @@ def array!(collection = [], *attributes)
   #
   #   json.(@person, :name, :age)
   def extract!(object, *attributes)
-    if ::Hash === object
-      _extract_hash_values(object, attributes)
-    else
-      _extract_method_values(object, attributes)
+    attributes.each do |key|
+      _set_value key, _extract_value(object, key)
     end
   end
 
@@ -252,12 +250,8 @@ def target!
 
   private
 
-  def _extract_hash_values(object, attributes)
-    attributes.each{ |key| _set_value key, object.fetch(key) }
-  end
-
-  def _extract_method_values(object, attributes)
-    attributes.each{ |key| _set_value key, object.public_send(key) }
+  def _extract_value(object, attribute)
+    object.respond_to?(attribute) ? object.public_send(attribute) : object.fetch(attribute)
   end
 
   def _merge_block(key)

test/jbuilder_test.rb

@@ -35,6 +35,17 @@ def initialize(name, age)
   end
 end
 
+class PersonWithHash
+  attr_reader :name, :collection
+
+  def initialize(name, age)
+    @collection = { age: age }
+    @name = name
+  end
+
+  delegate :[], :fetch, to: :@collection
+end
+
 class RelationMock
   include Enumerable
 
@@ -121,6 +132,17 @@ class JbuilderTest < ActiveSupport::TestCase
     assert_equal 34, result['age']
   end
 
+  test 'extracting from object with internal hash' do
+    person = PersonWithHash.new('David', 32)
+
+    result = jbuild do |json|
+      json.extract! person, :name, :age
+    end
+
+    assert_equal 'David', result['name']
+    assert_equal 32, result['age']
+  end
+
   test 'nesting single child with block' do
     result = jbuild do |json|
       json.author do