ScopedAttrAccessor

Adds scoped accessors to ruby. You can create writers, readers and accessors in either private or protected scope. Does not affect the scope of code that comes afterward. You can extend a single class (and its subclasses) with scoped accessors, or you can extend ruby's entire class hierarchy.

Installation

Add this line to your application's Gemfile:

gem 'scoped_attr_accessor'

And then execute:

$ bundle

Or install it yourself as:

$ gem install scoped_attr_accessor

Usage

You can add scoped accessors to a single class (and its children) by directly extending ScopedAttrAccessor in your class:

require 'scoped_attr_accessor'

class Primate
  extend ScopedAttrAccessor
  private_attr_accessor :some_weird_primate_only_counter
  protected_attr_reader :some_weird_counter
end

class Monkey < Primate
  # Monkey can define its own scoped accessors because Primate
  # extended the module.
  private_attr_reader :get_weird_monkey_only_stuff_here
  private_attr_writer :put_weird_monkey_only_stuff_here

  # use our inherited, protected reader
  def sufficiently_weird?
    some_weird_counter > 42
  end
end

Alternately, if you require scoped_attr_accessor/include, ruby's Object class will be extended with ScopedAttrAccessor making all classes able to have protected and private accessors.

require 'scoped_attr_accessor/include'

class Primate
  private_attr_accessor :private_primate_counter
end

Avoid Dependency Infection

The '/include' form of this gem is a ruby-wide monkeypatch. Please remember that it's perfectly fine to use it this way in your own applications, but quite rude to use it this way in a library. People who use your library would then be infected by this monkeypatch as well. Not cool.

If you use scoped accessors in a gem or library of your own, please consider using the non-include version, or, in Ruby 2.0, use refinements to confine the include patch to your library.

Ruby Versions

Tested to work on Ruby 1.9.3 and 2.0.

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Write tests for your feature or bug fix
4. Commit your changes (git commit -am 'Add some feature')
5. Push to the branch (git push origin my-new-feature)
6. Create new Pull Request

Why Oh Why Does This Exist?!?

At the time of this writing (April 2013), the ruby community in general is somewhat divided on the meaning of the concept of privacy in ruby. For some, especially those who come from Java, C++, VB, or some other language that enforces encapsulation with privacy, ruby's ability to get around privacy means that encapsulation cannot be enforced. Most of us (I have counted myself in this camp until now) have discarded the use of privacy in ruby altogether, as if it were nothing more than a half-hearted nod to other languages' encapsulation practices. Make everything public, we say; since everything's ultimately public anyway, using the private keyword is merely a speedbump which adds no security but does add hassle and headache.

I am becoming more and more aware of a number of rubyists who consider the use of private and protected methods in ruby to be a useful way to communicate to the reader that the code is highly volatile, under question, subject to change or outright removal, etc., and that for these reasons the code should not be surfaced to the public API of the class. They ALSO consider the private keyword to be merely a speedbump, but one which communicates that maybe you should slow down a bit before trying to access these portions of code. Furthermore, making these methods private or protected makes them "exemplary" to maintainers of the code, meaning that a maintainer will understand the intent of the privacy, and be less likely to accidentally create an external dependency on on a method that should have been kept private.

Another way of looking at this difference of opinion is that the old way of thinking is that private is there to protect my code from your prying eyes, which implies that I think I am smarter than every programmer ever, even all the ones who come from the future. It also means, at least in ruby, that I think hiding stuff inside a wet paper bag is a pretty good way of securing such code from you future programmers. This new way of thinking admits to the wet paper bag, but more importantly it reverses the direction of the protection: it is only a speedbump, but it is there to protect YOU, a smart future programmer, from code that I, a programmer from the past who knows he will never be as dumb as he is right now, wrote and got working but it's volatile and dangerous to depend upon. You may figure out a way to use that code safely, and if you do, then by all means cut through that paper bag.

I have become swayed by this second way of thinking, but I find that it falls short in one key area: accessors. It is easy to create a private method in ruby, but creating a private accessor method is actually a bit tortuous. As a result, I see programmers who strongly believe in using privacy to communicate undependable interfaces frequently making one of two bad tradeoffs: they either use instance variables or public accessors for their private variables. These variables are not dependable, at least from a "stable interface" standpoint, so both solutions are suboptimal. While instance variables communicate privacy, they force the class to depend on its own undependable internals. Making an accessor allows the class to create an internal interface to isolates itself from its own undependable internals, but by making it public the communication to the maintainer is that other classes can and should depend on that interface.

What is needed is a clean, easy, elegant way to create private and protected accessors, so that classes can create internal interfaces to their instance variables, reducing their exposure to their own volatility WITHOUT communicating that interface publically.

We need a clean and easy way to create private and protected accessors in ruby. My goal with this gem, then, is to create such a way, so that those who wish to communicate "this variable is undependable and it should be kept isolated for now" can do so easily.