ivar_encapsulation¶ ↑

For some reason the direct manipulation of instance variables in Ruby has bothered me for a long time. But not until I read more about Smalltalk did I quite appreciate why that was. Compared to directly reading from or writing to the instance variables, using getters and setters also inside the class feels a lot cleaner, at least to me. Alas one doesn’t always want to expose the methods generated by attr_* to the outside world, so I found myself repeatedly writing code similar to this:

attr_accessor :foo
private :foo=

While it certainly gets the job done, it’s a bit cumbersome in the long run, so I decided to write this gem as an alternative to the available attr_* methods.

A conflicted relationship with instance variables and Ruby 2.0+.

ivar_encapsulation can be installed via RubyGems.

$ gem install ivar_encapsulation

It only works on 2.0+ and I generally only test it with the most current Ruby release.

The most simple case is defining a purely internal attribute (both the getter and setter will be private):

class Foo
  attribute :foo
end

Of course this also works for several attributes at the same time:

attribute :foo, :bar, :baz

For the grammatically anal like yours truly, attribute is aliased to attributes, so the above could also be written thus:

attributes :foo, :bar, :baz

Now for a more interesting use case:

attribute foo, getter: true

This will define an attribute with a public getter method (foo), while the setter (foo=) remains private. Essentially this is the same as doing the following:

attr_accessor :foo
private :foo=

Once again this works for several attributes at the same time:

attribute :foo, :bar, :baz, getter: true

For completeness’ sake, you can also define a private getter and a public setter, although I don’t think I ever needed this specific case:

attribute :foo, setter: true

Last but not least there’s the option to have both the getter and the setter as public methods, which is essentially the same as attr_accessor, although in a more explicit fashion. If you bother to use this gem at all, you probably want to define all your attributes in a consistent fashion:

attribute :foo, getter: true, setter: true

This is how your class definitions will look when using this gem:

class Foo
  attributes :foo, :bar                              # private getters and setters
  attribute :read_only, getter: true                 # public getter, private setter
  attribute :full_access, getter: true, setter: true # public getter and setter

  def initialize(foo)
    self.foo = foo
    ...
  end

  ...

end

• Being able to supply getters and setters as procs?

This project was created by Michael Kohl. He can be reached via email at citizen428 at gmail.com.

Copyright © 2013 Michael Kohl

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