Move descendant_get from Object to Class

This is technically a breaking change, but it really wasn't possible to
call this on Objects previously.  Most callers called this on Class.

Fixes #62

README.md

@@ -47,6 +47,7 @@ MoreCoreExtensions are a set of core extensions beyond those provided by ActiveS
 #### Class
 
 * core_ext/class/hierarchy.rb
+  * `#descendant_get` - Returns the descendant with a given name
   * `#hierarchy` - Returns a tree-like Hash structure of all descendants.
   * `#lineage` - Returns an Array of all superclasses.
   * `#leaf_subclasses` - Returns an Array of all descendants which have no subclasses.
@@ -82,8 +83,6 @@ MoreCoreExtensions are a set of core extensions beyond those provided by ActiveS
 
 #### Object
 
-* core_ext/module/descendants.rb
-  * `#descendant_get` - Returns the descendant with a given name
 * core_ext/module/namespace.rb
   * `#in_namespace?` - Returns whether or not the object is in the given namespace
 

lib/more_core_extensions/core_ext/class/hierarchy.rb

@@ -3,6 +3,16 @@
 
 module MoreCoreExtensions
   module ClassHierarchy
+    #
+    # Retrieve a descendant by its name
+    #
+    def descendant_get(desc_name)
+      return self if desc_name == name || desc_name.nil?
+      klass = descendants.find { |desc| desc.name == desc_name }
+      raise ArgumentError, "#{desc_name} is not a descendant of #{name}" unless klass
+      klass
+    end
+
     # Returns a tree-like Hash structure of all descendants.
     #
     #   require 'socket'

lib/more_core_extensions/core_ext/object.rb

@@ -1,3 +1,2 @@
 require 'active_support/core_ext/object/blank'
 require 'more_core_extensions/core_ext/object/namespace'
-require 'more_core_extensions/core_ext/object/descendants'

spec/core_ext/class/hierarchy_spec.rb

@@ -1,6 +1,24 @@
 require 'socket' # for a more interesting hierarchy for specs
 
 describe Class do
+  context "#descendant_get" do
+    it "returns self if specified" do
+      expect(IO.descendant_get("IO")).to eq(IO)
+    end
+
+    it "returns a direct descendant" do
+      expect(IO.descendant_get("BasicSocket")).to eq(BasicSocket)
+    end
+
+    it "returns a transitive descendant" do
+      expect(IO.descendant_get("IPSocket")).to eq(IPSocket)
+    end
+
+    it "raises an error if no descendant is found" do
+      expect { IO.descendant_get("Foo") }.to raise_error(ArgumentError, "Foo is not a descendant of IO")
+    end
+  end
+
   it "#hierarchy" do
     expect(IO.hierarchy).to eq(
       BasicSocket => {