case and when in Ruby

Pattern dispatch with ===: ranges, classes and regexps all match.

# case matches with ===, so ranges, classes and regexps all work
def describe(value)
  case value
  when nil then "nothing"
  when 1..10 then "small number"
  when Integer then "number #{value}"
  when /\Arb/ then "starts with rb"
  when String then "#{value.length} characters"
  else "unknown"
  end
end

puts describe(nil)
puts describe(7)
puts describe(42)
puts describe("rbenv")
puts describe("typestar")

How it works

1. case compares with ===, so branches can be types or patterns.
2. when 1..10 catches small numbers before Integer sees them.
3. A regexp branch matches strings starting with rb.
4. then keeps single-expression branches on one line.

Keywords and builtins used here

• Integer
• String
• case
• def
• describe
• else
• end
• puts
• then
• when

The run, in numbers

Lines

17

Characters to type

393

Tokens

86

Three-star pace

85 tpm

At the three-star pace of 85 tokens a minute, this run takes about 61 seconds.

Type this snippet

Step 2 of 3 in Control flow, step 8 of 29 in Language basics.

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