Code snippet showing how to define public and private instance methods in Ruby.

public_and_private_instance_methods.rb

class Car
  attr_reader :mileage

  def initialize
    @mileage = 0
  end

  def drive
    update_mileage
  end

  private

  def update_mileage
    @mileage += 1
  end
end

# => car = Car.new
# #<Car:0x005..>
#
# => car.drive
# 1
#
# => car.update_mileage
# private method `update_mileage' called for #<Car:0x005..>
#
# => car.mileage
# 1