Ruby switch outputting unexpected value

Question

I don't work in Ruby day-to-day, but I'm attempting to brush up on it. On exercism.io, there's an exercise I'm attempting to complete and the solution I came up with isn't working. Here's the test code:

class ResistorColorDuoTest < Minitest::Test
  def test_brown_and_black
    # skip
    assert_equal 10, ResistorColorDuo.value(["brown", "black"])
  end
end

This is the solution I came up with:

module ResistorColorDuo
    def self.value(colors)
        case colors
        when (colors - ["brown", "black"]).empty?
            10
        else
            -1
        end
    end
end

The output from the method is -1. I can't figure out what I've fouled up. Any suggestions are greatly appreciated. Thank you for reading.

Tip: For simple arrays of single words use `%w[ brown black ]`. — tadman, Nov 08 '20 at 19:51

score 4 · Accepted Answer · answered Nov 08 '20 at 14:17

4

You're using case like it was an if.

(colors - ["brown", "black"]).empty?

evalutes to true so true is compared to your colors

switch to if-else

def self.value(colors)
  if (colors - ["brown", "black"]).empty?
    10
  else
    -1
  end
end

answered Nov 08 '20 at 14:17

Ursus

29,643
3
33
50

1

Thank you. I'm going to be throwing more stuff at it, but that gets the job done. Thank you so much for your prompt reply. It's greatly appreciated. – Adrian Nov 08 '20 at 14:19
My pleasure Sir – Ursus Nov 08 '20 at 14:19

Ben Stephens · Answer 2 · 2020-11-08T21:16:25.230

2

Based on: https://stackoverflow.com/a/42269911/14454939

colors = ["brown", "black"]

case
when (colors - ["brown", "black"]).empty?
    10
else
    -1
end
# => 10

colors = ["brown", "blue"]

case
when (colors - ["brown", "black"]).empty?
    10
else
    -1
end
# => -1

Edit: I didn't really think of it until now, but is there a reason you can't do?:

colors = ["brown", "blue"]

case colors
when ["brown", "black"]
    10
when ["brown", "blue"]
    20
else
    -1
end
# => 20

or if order shouldn't matter:

colors = ["brown", "blue"]

case colors.sort
when ["black", "brown"] #.sort if you don't want to sort manually
    10
when ["blue", "brown"]
    20
else
    -1
end
# => 20

edited Nov 08 '20 at 21:16

answered Nov 08 '20 at 14:47

Ben Stephens

3,303
1
4
8

Correct, but using `case` like this offers very little advantage over a more conventional `if` / `else` chain. – tadman Nov 08 '20 at 19:50
@tadman True. I've added a couple of more case-y things in case they help. – Ben Stephens Nov 08 '20 at 21:26

Ruby switch outputting unexpected value

2 Answers2