Symbol#to_proc with custom methods

Question

I like how in Ruby you can pass methods as blocks like so using Symbol#to_proc:

[1.0, 2.0, 3.0].map(&:to_i)
#=> [1, 2, 3]

Answer 1

You would have to define times_three on Integer or Numeric.

Symbol to Proc explained by Peter Cooper: https://www.youtube.com/watch?v=aISNtCAZlMg

Answer 2

class Integer
  def times_three
    return self * 3
  end
end

Now, because times_three is now a method of the Integer class, you can do symbol to proc...

[1, 2, 3].map(&:times_three)

If you want to access a method that isn't part of the object's class but acts on an object, you need to pass the object as an argument to the method...

def times_three(x)
  x * 3
end

[1, 2, 3].map{|i| times_three(i) }

the symbol to proc needs to use the object as a receiver.

[1, 2, 3].map(&:some_action)

is equivalent to

[1, 2, 3].map{|i| i.some_action}