s="Hola!"

#s is an object from what?
puts s.class
#output: String

#what is the name of this class ?
puts s.class.name 
#output: String

#from what String  was inherited?
puts String.superclass #object is the parent class of 'em all!

#the included modules in String
p String.included_modules
#output: [Enumerable, Comparable, Kernel]

p Object.included_modules
#output: [Kernel]

#each object has a unique id.
s1="Hi"
puts s1.object_id  #6

s2="Hi"
puts s2.object_id  #8

s1="Hi"
s2=s1 #points to s1

puts s1.object_id #6
puts s2.object_id #6

p Math.constants
#output: ["E", "PI"]

#get the local variables
p local_variables
#output: ["s", "s1", "s2"]

$globString="What's up????"
$anotherGlobString="CRUEL, WORLD!"

#gets the global variables
p global_variables
#output
#["$FILENAME", "$LOADED_FEATURES", "$anotherGlobString", 
#  "$VERBOSE", "$globString", "$PROGRAM_NAME", "$LOAD_PATH", 
#  "$DEBUG", "$stdin", "$KCODE", "$stderr", "$stdout", "$defout", 
#  "$deferr", "$-I", "$`", "$-K", "$\\", "$_", "$!", 
#  "$\"", "$-a", "$-d", "$~", "[email protected]", "$?", "$>", 
#  "$=", "$<", "$:", "$0", "$.", "$/", "$,", "$-n", 
#  "$*", "$SAFE", "$+", "$-p", "$&", "$'", "$$", "$-l"]

p instance_variables # []

#get all of the methods in string
methodsAry=String.methods
p methodsAry
#output:
#["new", "superclass", "allocate", "inherited", "initialize_copy",
.....................
#  "class_eval", ">", "<", "private_class_method", 
, 
#  "protected_methods", "nil?", "freeze", "is_a?", "eql?"]

#instance methods
p String.instance_methods

#get the private methods.
p String.private_methods

[private|protected|public]_instance_methods

respond_to?(:methodName)

s="Hello"
puts s.respond_to?(:upcase) #true: can use upcase method 
puts s.respond_to?(:keys) #false: can't use keys method

class First < String
  
end

class Second < First
  
end

class Third < Second

end

c=Third

while c
  print(c) 
  print(" < ")
  c=c.superclass
  
end
puts