The Ruby Case Statement Cheatsheet

The Ruby case statement is simple enough to master:

case a
when 'A', 'B'
  puts 'A or B'
when 'C'
  puts 'A or B'
else
  puts 'Not A, B, or C'
end

When using regex (via documentation):

case "12345"
when /^1/
  puts "the string starts with one"
else
  puts "I don't know what the string starts with"
end

When you want to create more complex statements (via documentation):

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

You can also use a lambda in when for readability:

case a
when ->(n){n == 1 || n == 2}
  puts "a is one or two"
when when ->(n){n <= 3}
  puts "a is at least 3"
else
  puts "I don't know what a is"
end

Things to note:

• The , in when 'A', or 'B' means “or”
• The default block is under else
• when can accept regex or procs. For a full list of things you can do with when see things you can do ===.