PrivateAttrs

Introducing Private Attrs

The private_attrs gem is a quick addition to Ruby’s Class object that allows for defining private attribute methods.

Usage

class Crocodile
  private_attr_reader :temper

  def initialize(temper)
    @temper = temper
  end
end

Crocodile.new('angry').temper # => NoMethodError "private method 'temper' called for ...

But, why?

In short, because existing patterns to do this are ugly. This particular pattern violates the ‘Scissors Rule' of coding in that there is not a clear separation between public and private methods.

class Crocodile
  private

  attr_reader :temper

  public

  attr_reader :asleep

  def initialize(temper)
    @temper = temper
  end

  def bites?
    if angry? && !asleep?
  end

  private

  def angry?
    temper == 'angry'
  end

  def asleep?
    current_time = Time.now
    (current_time.hour >= 17) and (current_time.hour <= 21)
  end
end

This example is better but still not ideal as we want all of our attribute methods defined at the top of any given class.

class Truck

  attr_reader :transmission_type
  attr_reader :weight

  def initialize(wheel_count:, transmission_type:, weight:)
    @wheel_count = wheel_count
    @transmission_type = transmission_type
    @weight =  weight
  end

  def oversized
    wheel_count > 4
  end

  def driver_must_shift?
    transmission_type == :manual
  end

  private

  attr_reader :wheel_count
end

Other patterns are even worse…

class Pet

  attr_accessor :species
  private :species
  private :species=

  attr_reader :hairy
  private :hairy

  def initialize(species, hairy)
    #...
  end
end

Installation

Add this line to your application's Gemfile:

gem 'private_attrs'

And then execute:

$ bundle

Or install it yourself as:

$ gem install private_attrs

License

The gem is available as open source under the terms of the MIT License.