How to implement a "callback" in Ruby?

Question

I'm not sure of the best idiom for C style call-backs in Ruby - or if there is something even better ( and less like C ). In C, I'd do something like:

void DoStuff( int parameter, CallbackPtr callback )
{
  // Do stuff
  ...
  // Notify we're done
  callback( status_code )
}

Whats a good Ruby equivalent? Essentially I want to call a passed in class method, when a certain condition is met within "DoStuff"

Answer 1

The ruby equivalent, which isn't idiomatic, would be:

def my_callback(a, b, c, status_code)
  puts "did stuff with #{a}, #{b}, #{c} and got #{status_code}"
end

def do_stuff(a, b, c, callback)
  sum = a + b + c
  callback.call(a, b, c, sum)
end

def main
  a = 1
  b = 2
  c = 3
  do_stuff(a, b, c, method(:my_callback))
end

The idiomatic approach would be to pass a block instead of a reference to a method. One advantage a block has over a freestanding method is context - a block is a closure, so it can refer to variables from the scope in which it was declared. This cuts down on the number of parameters do_stuff needs to pass to the callback. For instance:

def do_stuff(a, b, c, &block)
  sum = a + b + c
  yield sum
end

def main
  a = 1
  b = 2
  c = 3
  do_stuff(a, b, c) { |status_code|
    puts "did stuff with #{a}, #{b}, #{c} and got #{status_code}"
  }
end