private_methods.rb

class Foo
  def this_fails
    puts self.bar
  end
 
  def this_works
    puts bar
  end
 
private
  def bar
    "Foo#bar"
  end
end
 
foo = Foo.new
foo.this_fails
NoMethodError: private method `bar' called for #<Foo:0x007fc68314e0a0>
 
foo.this_works
=> "Foo#bar"