Return Values

Prerequisites: Methods

Every Ruby method returns a value. By default it's the value of the last expression that ran.

def double(n)
  n * 2
end

result = double(21)
p result

Returning early with return

return exits the method immediately. It's most useful for guard clauses — checks at the top of a method that bail out early:

def discount(price, code)
  return price if code.nil?
  return price * 0.9 if code == "SAVE10"

  price
end

p discount(100, nil)
p discount(100, "SAVE10")
p discount(100, "WRONG")

100
90.0
100

Guard clauses keep the main logic un-indented and easy to read, instead of wrapping it in nested ifs.

Returning several values

Return an array, and the caller can unpack it into several variables:

def min_max(numbers)
  [numbers.min, numbers.max]
end

low, high = min_max([4, 9, 1])
puts "#{low} to #{high}"

1 to 9

puts is not return

puts prints a value; it doesn't return it. puts itself returns nil:

def shout(word)
  puts word.upcase
end

result = shout("hi")
p result

HI
nil

Common mistakes

Ending a method with puts and then trying to use its result. Let methods return values, and print them where they're called.
An if with no else as the last line returns nil when the condition is false.

Practice

Write grade(score) that returns "pass" or "fail" (pass is 50 or more) using a guard clause, and print the results for 72 and 31.

Show solution

def grade(score)
  return "pass" if score >= 50

  "fail"
end

puts grade(72)
puts grade(31)