1 files changed, 54 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/class/subclasses.rb b/activesupport/lib/active_support/core_ext/class/subclasses.rb
new file mode 100644
index 0000000000..56fb46a88d
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/class/subclasses.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+class Class
+  begin
+    # Test if this Ruby supports each_object against singleton_class
+    ObjectSpace.each_object(Numeric.singleton_class) { }
+
+    # Returns an array with all classes that are < than its receiver.
+    #
+    #   class C; end
+    #   C.descendants # => []
+    #
+    #   class B < C; end
+    #   C.descendants # => [B]
+    #
+    #   class A < B; end
+    #   C.descendants # => [B, A]
+    #
+    #   class D < C; end
+    #   C.descendants # => [B, A, D]
+    def descendants
+      descendants = []
+      ObjectSpace.each_object(singleton_class) do |k|
+        next if k.singleton_class?
+        descendants.unshift k unless k == self
+      end
+      descendants
+    end
+  rescue StandardError # JRuby 9.0.4.0 and earlier
+    def descendants
+      descendants = []
+      ObjectSpace.each_object(Class) do |k|
+        descendants.unshift k if k < self
+      end
+      descendants.uniq!
+      descendants
+    end
+  end
+
+  # Returns an array with the direct children of +self+.
+  #
+  #   class Foo; end
+  #   class Bar < Foo; end
+  #   class Baz < Bar; end
+  #
+  #   Foo.subclasses # => [Bar]
+  def subclasses
+    subclasses, chain = [], descendants
+    chain.each do |k|
+      subclasses << k unless chain.any? { |c| c > k }
+    end
+    subclasses
+  end
+end