illustrating ruby method visibility machanism

method_visibility.rb

class Bla
  def a
    "a"
  end

  def b
    self.a
  end

  def c
    a
  end
end

class Bla0 < Bla
end

b  = Bla.new
b0 = Bla0.new

Bla.send(:public, :a)
b.a # => "a"
b.b # => "a"
b.c # => "a"
b0.a # => "a"
b0.b # => "a"
b0.c # => "a"

Bla.send(:protected, :a)
b.a # => NoMethodError
b.b # => "a"
b.c # => "a"
b0.a # => NoMethodError
b0.b # => "a"
b0.c # => "a"

Bla.send(:private, :a)
b.a # => NoMethodError
b.b # => NoMethodError
b.c # => "a"
b0.a # => NoMethodError
b0.b # => NoMethodError
b0.c # => "a"