ValueObject

A very small library to help you define and create immutable value objects.

Why?

Mainly to reduce the amount of code I needed for ActiveRecord composed_of classes. ValueObjects are designed with composed_of in mind; they will:

• happily accept nil for their fields, unlike Values.
• allow multiple levels of subclassing -- if you want a value object which is like some other class of value object (ie, it has all of the other object's fields and methods) but will some additional field or method, you can simply subclass it.

How to use

Require it

require 'value_object'

Subclass it

class Person < ValueObject::Base
  has_fields :height, :weight
end

Create a value object with positional arguments

tom = Person.new(176, 75)
dick = Person.new(160, 60)

Create a value object with a hash

harry = Person.new(:height => 176, :weight => 75)

Read their attributes

tom.height        # => 176
dick.weight       # => 60

Test whether value objects are equal

tom == dick       # => false
tom == harry      # => true

Test for emptiness

Person.new(nil, nil).empty?    # => true

You can even subclass them again!

class Superhero < Person
  has_fields :power
end

superman = Superhero.new('6 foot 3', '235 lbs', 'flies')

superman.height     # => '6 foot 3'
superman.weight     # => '235 lbs'
superman.power      # => 'flies'