How do I only allow an argument in a Ruby function to be a certain type?

Question

For example, if I have

def function(arg)
  #do stuff
end

how do I only allow arg to be an Array? I could do

def function(arg)
  if arg.class != 'Array'
    return 'Error'
  else
    #do stuff
  end
end

but is there any better way of doing this?

Answer 1

You can't do def function(Array arg) like in other languages, but you can replace four lines of your second snippet by a single one:

def function(arg)
  raise TypeError unless arg.is_a? Array
  # code...
end