[Toutouxc]

No, passing a symbol and sending is a different mechanism.

The send method is basically the same thing as calling a method by name, as in "obj.foo" == "obj.send(:foo)". If you only pass a symbol into your "caller" method, the symbol goes through the normal lookup: does the receiving object respond to this? If yes, then that implementation (at that exact moment) is called, if not, you get a method_missing.

You're right that that's not how you do first-class functions in ruby. Your example in ruby would be:

  def get_and_call(fn, x)
    fn.call(x)
  end

  def upcasinator_method(str)
    str.upcase
  end

  upcasinator_lambda = lambda {|str| str.upcase}

  get_and_call(upcasinator_lambda, 'foobar')
  => "FOOBAR"

  get_and_call(method(:upcasinator_method), 'foobar')
  => "FOOBAR"

As you can see there are two ways to do that -- either you create a Proc (a lambda if you care about arity), which is the first class function in Ruby, and you call that, or you define a method (but that's a method, an OOP concept, a procedure that implicitly operates on an object), you get a hold of it using the "method" method and then you call it.