klass.rb

# global obj instance (instance of Object class)
puts self
# instance of class Class, so we can have objects of this class
class Klass

  @foo = 'bar'
  puts self #(Klass itself)
  # we create instance method
  # or (more precisly) method in current self
  def foo
    @foo = 'baz'
    puts self #(instance of Klass class)
  end

  # we create class method
  # or (more precisly) method in obj class
  def self.foo
    puts 'bla'
  end

  def self.has_many
    puts 'bla'
  end

  has_many
end

Klass.new.foo

obj.rb

class Obj
  # $glob
  # @@class_hier
  # @class_instance_variable
  # @inst_variable
  def set_setter(arg)
    @foo = arg
  end
  def setter=(arg)
    @foo = arg
  end

  def print_foo
    puts @foo
  end


  def <=>(other)

  end

  #tricky:
  def tricky
    # proper
    # self.setter = 'blafoo'
    # here ruby create local var, not use setter= method
    setter = 'blafoo'
  end

  def tricky2
    # since there is no print_foo local var, ruby uses self here
    print_foo
  end

  def block_with_yield(a) # def block(a, func)
    yield a               #   func(a)
  end

  def block_with_lambda(a, &blk) # def block(a, func)
    blk.call(a)                  #   func(a)
  end
end