=begin

Class < Module < Object
Kernel module
Object includes Kernel
   Kernel instance methods documented with Object
   Kernel module methods documented in Kernel.
      They are called without a receiver.

Ruby classes are dynamic.  When we define a class an object of type Class is created and assigned to a constant with the name of the class.

=end

class A
                                # in an A instance here
   p self                       # p is module method in Kernel
                                #  supposed to use inspect and separator
   Kernel.p self                # alternative
   p self.inspect               # inspect in Object
                                #   uses to_s if not overridden
   p self.to_s                  # to_s in Object, returns string rep
   p self.class                 # class is an Object method
   p self.name                  # name is a Module method
   s = "house"
   p s.length                   # class def is executable
   p self.const_defined? "PI"   # Module instance method, Class < Module
end

p A.const_defined? "PI"         # Module instance method

a = A.new
#  p a.const_defined?           # variable a instance of A, not Class