Hi Sirs.

There is a difference between a bunch of methods that appear that they to the same job, but they won't.

The methods instance_of?, is_a? and kind_of? do related jobs, but not the same job.

For example is_a? and kind_of? do the same job, they return true if the caller is an instance of the method argument, if the caller is an instance of every superclass in his inheritance tree or if the argument method is a module included in the caller.

The instance_of? is more specific, it returns true just if the caller is an instance of the method argument.

Let me show some examples:

module Hand
end

class Animal
end

class Mamal < Animal
  include Hand
end

class Dog < Mamal
end

dog = Dog.new

puts dog.instance_of?(Dog)    # true
puts dog.instance_of?(Mamal)  # false
puts dog.instance_of?(Animal) # false
puts dog.instance_of?(Hand)   # false

puts dog.is_a?(Dog)    # true
puts dog.is_a?(Mamal)  # true
puts dog.is_a?(Animal) # true
puts dog.is_a?(Hand)   # true 

Remember that is_a? and kind_of? do the same job.

See you.