option-parameter.md

Option Parameter

A method has the information needed to make a decision, but doesn't act on it. Instead, it passes the information to some other method via an Option Parameter, and demands that the other method act on it.

When a method takes an Option Parameter, it's a good sign that the method has Multiple Responsibilities that should be separated.

What It Looks Like

In the code below, the capitalize parameter to container is an Option Parameter.

def line_of_song(n)
  "#{container(n, true)} of beer on the wall, #{container(n)} of beer."
end

def container(count, capitalize = false)
  string =
    case count
    when 0
      "no more bottles"
    when 1
      "one more bottle"
    else
      "#{count} bottles"
    end

  if capitalize
    string.capitalize
  else
    string
  end
end

Why It Hurts

In the example above, the container method has been assigned too many responsibilities. The capitalization logic should properly live in line_of_song, which knows when the strings should be capitalized.

How To Fix It

Use Move Statements to Callers to get the excess responsibilities out of the method that has too many. Then remove the unused parameter(s).