Add `Hash#map_values` to ActiveSupport

Didn't get a chance to convert existing code, I'll skim through the code
base to make use of this later this afternoon.

1 files changed, 49 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/hash/transform_values_test.rb b/activesupport/test/core_ext/hash/transform_values_test.rb
new file mode 100644
index 0000000000..4449c94701
--- /dev/null
+++ b/activesupport/test/core_ext/hash/transform_values_test.rb
@@ -0,0 +1,49 @@
+require 'abstract_unit'
+require 'active_support/core_ext/hash/indifferent_access'
+require 'active_support/core_ext/hash/transform_values'
+
+class TransformValuesTest < ActiveSupport::TestCase
+  test "transform_values returns a new hash with the values computed from the block" do
+    original = { a: 'a', b: 'b' }
+    mapped = original.transform_values { |v| v + '!' }
+
+    assert_equal({ a: 'a', b: 'b' }, original)
+    assert_equal({ a: 'a!', b: 'b!' }, mapped)
+  end
+
+  test "transform_values! modifies the values of the original" do
+    original = { a: 'a', b: 'b' }
+    mapped = original.transform_values! { |v| v + '!' }
+
+    assert_equal({ a: 'a!', b: 'b!' }, original)
+    assert_same original, mapped
+  end
+
+  test "indifferent access is still indifferent after mapping values" do
+    original = { a: 'a', b: 'b' }.with_indifferent_access
+    mapped = original.transform_values { |v| v + '!' }
+
+    assert_equal 'a!', mapped[:a]
+    assert_equal 'a!', mapped['a']
+  end
+
+  # This is to be consistent with the behavior of Ruby's built in methods
+  # (e.g. #select, #reject) as of 2.2
+  test "default values do not persist during mapping" do
+    original = Hash.new('foo')
+    original[:a] = 'a'
+    mapped = original.transform_values { |v| v + '!' }
+
+    assert_equal 'a!', mapped[:a]
+    assert_nil mapped[:b]
+  end
+
+  test "default procs do not persist after mapping" do
+    original = Hash.new { 'foo' }
+    original[:a] = 'a'
+    mapped = original.transform_values { |v| v + '!' }
+
+    assert_equal 'a!', mapped[:a]
+    assert_nil mapped[:b]
+  end
+end