Ryan Bigg

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The method method

20 Jan 2023

The method method in Ruby is one of my favourite methods in Ruby. It gives you an object that represents an underlying method. It’s helpful for demonstrating that integer addition in Ruby is a method call:

=> #<Method: Integer#+(_)>

Where is this method defined?

With this method method, you can find out where a method is defined, if it is defined in Ruby code anywhere:

=> ["...activerecord-x.x.x/lib/active_record/core.rb", 337]

Then I can look at this source code within the Active Record gem to find out how find works.

Call me, maybe?

Methods can also be passed in place of traditional block arguments:

class Maths
  def self.square(num)
    num ** 2

square = Maths.method(:square)

[1, 2, 3, 4].map(&square)

The map syntax here is short-hand for:

[1, 2, 3, 4].map { |number| square.call(number) }

Which is exactly the same behaviour that a Proc has:

a_proc = -> (num) { num ** 2 }
[1, 2, 3, 4].map(&square)

More documentation

You can find more about the Method class here. You can even find out why this code returns true:

def moo(arg) arg == 3; end

number = 3
case number
when method(:moo)