question regarding is_a? and kind_of?

gistfile1.txt

# running on irb
# why is is_a? and kind_of methods work as expected on instances and not on the class itself
# --- bcuz Foo.class is a Class not a String
# how to differentiate between inheritance and composition relationship 

module Baz
end

class Bar < String
end

class Foo < Bar
  include Baz
end
 
f = Foo.new
f.is_a? String #true 
f.kind_of? String #true 

Foo.kind_of? String #false 
Foo.is_a? String #false 

Foo.ancestors
# [Foo, Baz, Bar, String, Enumerable, Comparable, Object, Kernel] 

# thanks to @xxxxxxx and @krainboltgreene pointing it out on #ruby irc
# TODO: how to differentiate between inheritance and composition relationship?
Foo < Bar # true
Foo < Baz # true
Foo.ancestors.include? String #true