Ruby’s case statement calls the === method on the argument to each of the when statements

So, this example:

case my_number
  when 6883
    :prime
end

Will execute 6883 === my_number

This is all fine and dandy, because the === method on a Fixnum instance does what you’d expect in this scenario.

However, the === method on the Fixnum class does something different. It’s an alias of is_a?

That is cute, because it allows you to do this:

case my_number
  when Fixnum
    "Easy to memorize"
  when Bignum
    "Hard to memorize"
  end

But it won’t work as you might expect in this scenario:

my_type = Fixnum
case my_type
  when Fixnum
    "Fixed number"
end

This won’t work because Fixnum === Fixnum returns false because the Fixnum class is not an instance of Fixnum.

My workaround for this is to convert it to a string first. Not sure if that’s the best solution, but it works for me(tm).

my_type = Fixnum
case my_type.to_s
  when "Fixnum"
    "Fixed number"
end