Ruby Tip #3: Matching on an Object’s Class in a Case Expression

From time to time you might want to take different actions depending on an object’s class. One handy way to do so is with a case expression:

case object
when Fixnum then puts 'Object is an integer number'
when String then puts 'Object is a string'
when Hash then puts 'Object is a hash'
end

Behind the scenes this is transformed to:

if Fixnum === object
  puts 'Object is an integer number'
elsif String === object
  puts 'Object is a string'
elsif Hash === object
  puts 'Object is a hash'
end

A lot of people seem to make the following mistake, so beware:

# WRONG - Class === Class will return false
case object.class
when Fixnum then puts 'Object is an integer number'
when String then puts 'Object is a string'
when Hash then puts 'Object is a hash'
end

Hopefully you’ll find this small tip useful.