Let's say that you want to use a given object if the object is an array; however, if the object is not an array (meaning it is a string, or a fixnum, etc.), then you do not want to use it.

You can use the .class method with conditional logic to determine this. The catch is you need to also convert the .class result into a string, like this:

a = [1, 2 , 3]
if a.class.to_s == 'Array'
  puts "It is an array"
else
  puts "It is not an array"
end

The above code would yield It is an array. If you leave out the .to_s, it would yield It is not an array.

ALTERNATE APPROACH:

You can use instance_of?. This returns true if the object is an instance of the given class, as in this example:

num = 10  
puts(num.instance_of? Fixnum)  #output true