Reflection does not report methods defined only in refinements
class C end module M refine C do def foo puts "C#foo in M" end end end using M c = C.new c.foo # prints "C#foo in M" c.send :foo p c.respond_to? :foo p c.methods.include?(:foo) p C.instance_methods.include?(:foo) p((c.method(:foo) rescue false)) __END__ Prints: C#foo in M C#foo in M false false false false
When the refinement M is used I think it would be less surprising if reflection methods (respond_to?, methods, method, instance_methods) report available methods including the ones coming from refinement.