Merge pull request #7007 from Mik-die/hash_extract

make Hash#extract! more symmetric with Hash#slice

activesupport/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Hash#extract! returns only those keys that present in the receiver.
+
+        {:a => 1, :b => 2}.extract!(:a, :x) # => {:a => 1}
+
+    *Mikhail Dieterle*
+
+*   Hash#extract! returns the same subclass, that the receiver is. I.e.
+    HashWithIndifferentAccess#extract! returns HashWithIndifferentAccess instance.
+
+    *Mikhail Dieterle*
+
 *   Optimize ActiveSupport::Cache::Entry to reduce memory and processing overhead. *Brian Durand*
 
 *   Tests tag the Rails log with the current test class and test case:

activesupport/lib/active_support/core_ext/hash/slice.rb

@@ -32,9 +32,9 @@ def slice!(*keys)
 
   # Removes and returns the key/value pairs matching the given keys.
   #
-  #   { a: 1, b: 2, c: 3, d: 4 }.extract!(:a, :b)
-  #   # => {:a => 1, :b => 2}
+  #   { a: 1, b: 2, c: 3, d: 4 }.extract!(:a, :b) # => { a: 1, b: 2 }
+  #   { a: 1, b: 2 }.extract!(:a, :x) # => { a: 1 }
   def extract!(*keys)
-    keys.each_with_object({}) { |key, result| result[key] = delete(key) }
+    keys.each_with_object(self.class.new) { |key, result| result[key] = delete(key) if has_key?(key) }
   end
 end

activesupport/test/core_ext/hash_ext_test.rb

@@ -723,8 +723,32 @@ def test_indifferent_slice_access_with_symbols
   def test_extract
     original = {:a => 1, :b => 2, :c => 3, :d => 4}
     expected = {:a => 1, :b => 2}
+    remaining = {:c => 3, :d => 4}
 
-    assert_equal expected, original.extract!(:a, :b)
+    assert_equal expected, original.extract!(:a, :b, :x)
+    assert_equal remaining, original
+  end
+
+  def test_extract_nils
+    original = {:a => nil, :b => nil}
+    expected = {:a => nil}
+    extracted = original.extract!(:a, :x)
+
+    assert_equal expected, extracted
+    assert_equal nil, extracted[:a]
+    assert_equal nil, extracted[:x]
+  end
+
+  def test_indifferent_extract
+    original = {:a => 1, 'b' => 2, :c => 3, 'd' => 4}.with_indifferent_access
+    expected = {:a => 1, :b => 2}.with_indifferent_access
+    remaining = {:c => 3, :d => 4}.with_indifferent_access
+
+    [['a', 'b'], [:a, :b]].each do |keys|
+      copy = original.dup
+      assert_equal expected, copy.extract!(*keys)
+      assert_equal remaining, copy
+    end
   end
 
   def test_except

guides/source/active_support_core_extensions.md

@@ -2867,8 +2867,16 @@ The method `extract!` removes and returns the key/value pairs matching the given
 
 ```ruby
 hash = {:a => 1, :b => 2}
-rest = hash.extract!(:a) # => {:a => 1}
-hash                     # => {:b => 2}
+rest = hash.extract!(:a, :x) # => {:a => 1}     # non-existing keys are ignored
+hash                         # => {:b => 2}
+```
+
+The method `extract!` returns the same subclass of Hash, that the receiver is.
+
+```ruby
+hash = {:a => 1, :b => 2}.with_indifferent_access
+rest = hash.extract!(:a).class
+# => ActiveSupport::HashWithIndifferentAccess
 ```
 
 NOTE: Defined in `active_support/core_ext/hash/slice.rb`.