gistfile1.txt

# Including a module included in a superclass is ignored
>> module Foo; end
=> nil
>> class Numeric; include Foo; end
=> Numeric
>> Float.ancestors
=> [Float, Precision, Numeric, Foo, Comparable, Object, Kernel]
>> class Float; include Foo; end
=> Float
>> Float.ancestors
=> [Float, Precision, Numeric, Foo, Comparable, Object, Kernel]

# But reversing the order of inclusion works as expected
>> module Foo; end
=> nil
>> class Float; include Foo; end
=> Float
>> Float.ancestors
=> [Float, Foo, Precision, Numeric, Comparable, Object, Kernel]
>> class Numeric; include Foo; end
=> Numeric
>> Float.ancestors
=> [Float, Foo, Precision, Numeric, Foo, Comparable, Object, Kernel]

# And so does including a dupe of the module!
>> module Foo; end
=> nil
>> class Numeric; include Foo; end
=> Numeric
>> Float.ancestors
=> [Float, Precision, Numeric, Foo, Comparable, Object, Kernel]
>> class Float; include Foo.dup; end
=> Float
>> Float.ancestors
=> [Float, #<Module:0x19bcd40>, Precision, Numeric, Foo, Comparable, Object, Kernel]