Question

Despite numerous attempts I am unable to create a method using the define_method() and supplying a method.

If I understand the documentation for the Module class that can be found here http://www.ruby-doc.org/core-1.9.3/Module.html I should be able to do either of the following:

define_method(symbol, method) → new_method

define_method(symbol) { block } → proc

I am able to use define_method(symbol) { block } however what I receive seems to be a method (not a proc as outlined on in the doc I linked to):

class M
  define_method(:hello) { puts "Hello World!"}
end

M.new.hello

My two concerns here are:
1. Doing the above I don’t seem to be receiving a proc despite the doc clearly stating that’s what I would get.
2. I have no clue how to supply a method for “define_method(symbol, method) → new_method”, I tried googling to no avail, not sure how to use this form of define_method.

If anyone could please shed any light on this that would be greatly appreciated! 🙂 Many thanks!

Answer 1

define_method does indeed return a Proc or a Method depending on usage.

In the first case, a Proc is returned:

class Test
  x = define_method :test_method { nil }
  puts x.inspect
end


Test.new.test_method

Running the above on the console outputs:

#<Proc:[e-mail]:3 (lambda)>

---

The second case returns an UnboundMethod, which is a type of Method:

class Test2 < Test
  y = define_method :test_method2, Test.instance_method(:test_method)
  puts y.inspect
end

Test2.new.test_method2

The above outputs

#<UnboundMethod: Test#test_method>

This is an extremely contrived example, and defining a method to pass to define_method isn’t really useful in this case, nor can I think of a case where it would be.