Make Mutex_m work with Module#prepend

README.md

@@ -34,10 +34,12 @@ obj.extend Mutex_m
 ```
 
 Or mixin Mutex_m into your module to your class inherit Mutex instance methods.
+You should probably use `prepend` to mixin (if you use `include`, you need to
+make sure that you call `super` inside `initialize`).
 
 ```ruby
 class Foo
-  include Mutex_m
+  prepend Mutex_m
   # ...
 end
 

lib/mutex_m.rb

@@ -51,6 +51,11 @@ def Mutex_m.define_aliases(cl) # :nodoc:
     cl.alias_method(:synchronize, :mu_synchronize)
   end
 
+  def Mutex_m.prepend_features(cl) # :nodoc:
+    super
+    define_aliases(cl) unless cl.instance_of?(Module)
+  end
+
   def Mutex_m.append_features(cl) # :nodoc:
     super
     define_aliases(cl) unless cl.instance_of?(Module)

test/test_mutex_m.rb

@@ -56,6 +56,49 @@ def test_initialize_no_args
     assert NoArgInitializeChild.new
   end
 
+  class PositionalArgInitializeParent
+    attr_reader :x
+
+    def initialize(x)
+      @x = x
+    end
+  end
+
+  def test_include
+    c = PositionalArgInitializeParent.dup
+    c.class_eval do
+      alias initialize initialize
+      def initialize(x)
+        @x = x
+        super()
+      end
+      include Mutex_m
+    end
+    o = c.new(1)
+    assert_equal(1, o.synchronize{o.x})
+  end
+
+  def test_prepend
+    c = PositionalArgInitializeParent.dup
+    c.prepend Mutex_m
+    o = c.new(1)
+    assert_equal(1, o.synchronize{o.x})
+  end
+
+  def test_include_sub
+    c = Class.new(PositionalArgInitializeParent)
+    c.include Mutex_m
+    o = c.new(1)
+    assert_equal(1, o.synchronize{o.x})
+  end
+
+  def test_prepend_sub
+    c = Class.new(PositionalArgInitializeParent)
+    c.prepend Mutex_m
+    o = c.new(1)
+    assert_equal(1, o.synchronize{o.x})
+  end
+
   def test_alias_extended_object
     object = Object.new
     object.extend(Mutex_m)