Case / Switch Statement in Ruby

Why is this here?

I always forget how to write case statements and always find myself looking it up. This is my note to future self on how to write case / switch statements in Ruby.

Syntax

Syntax for a case statement is as follows:

Ruby

case argument
when condition
  # do stuff
else
  # do stuff if nothing else meets the condition
end

“Else” is optional and represents the “default” case.

All case statements written in this syntax are compared with the === operator so be aware of that! === has slightly different semantics from == which can be found here:

This same === feature is what allows us to compare Regexs on Strings and other cool behavior. === is overriden by individual modules but is usually aliased to ==

Basic statement

Ruby

arg = "blah"
case arg
when /blah/
  puts "woah, what a blah!"
else
  puts "Theres no blah here!"
end

Adding multiple conditionals

Ruby

def fruit_identifier(fruit)
  case fruit
  when "orange", "grapefruit"
    puts "Woah! Thats some good citrus!"
  when "apple", "banana", "pear"
    puts "Just some normal fruits. Nothing to see here."
  end
end

One liners

Ruby

def one_line_case
  case "only_one"
  when "only_one" then puts "Look ma! One line!"
  end
end

if / else syntax

Ruby

a = 2
case
when a == 1, a == 2
  puts "a is one or two"
when a == 3
  puts "a is three"
else
  puts "I don't know what a is"
end