How to write a switch statement in Ruby

Question

How do I write a switch statement in Ruby?

Answer 1

Ruby uses the case expression instead.

case x when 1..5   "It's between 1 and 5" when 6   "It's 6" when "foo", "bar"   "It's either foo or bar" when String   "You passed a string" else   "You gave me #{x} -- I have no idea what to do with that." end 

Ruby compares the object in the when clause with the object in the case clause using the === operator. For example, 1..5 === x, and not x === 1..5.

This allows for sophisticated when clauses as seen above. Ranges, classes and all sorts of things can be tested for rather than just equality.

Unlike switch statements in many other languages, Ruby’s case does not have fall-through, so there is no need to end each when with a break. You can also specify multiple matches in a single when clause like when "foo", "bar".

Answer 2

case...when behaves a bit unexpectedly when handling classes. This is due to the fact that it uses the === operator.

That operator works as expected with literals, but not with classes:

1 === 1           # => true Fixnum === Fixnum # => false 

This means that if you want to do a case ... when over an object's class, this will not work:

obj = 'hello' case obj.class when String   print('It is a string') when Fixnum   print('It is a number') else   print('It is not a string or number') end 

Will print "It is not a string or number".

Fortunately, this is easily solved. The === operator has been defined so that it returns true if you use it with a class and supply an instance of that class as the second operand:

Fixnum === 1 # => true 

In short, the code above can be fixed by removing the .class from case obj.class:

obj = 'hello' case obj  # was case obj.class when String   print('It is a string') when Fixnum   print('It is a number') else   print('It is not a string or number') end 

I hit this problem today while looking for an answer, and this was the first appearing page, so I figured it would be useful to others in my same situation.