Case / Switch Statement in Ruby

#ruby #case #conditional

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:

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

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

Adding multiple conditionals

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

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

if / else syntax

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

Top comments (2)

Polar Humenn • May 25 '21

I never understood the reason why they just did not go with a defacto standard (switch, case, default)? It is quite annoying. I have to look this up all the time when I have to write some Ruby code. Sort of like Microsoft choosing a backslash for a file separator.