Provide equality comparison methods for objects based on their attributes.
By including this module, a class indicates that its instances have explicit general contracts for
hash methods. Specifically the
eql? contract requires that it implements an equivalence relation. By default, each instance of a class is equal only to itself. This is the right behaviour when you have distinct objects. However, it is the responsibility of any class to clearly define its equality. Failure to do so may prevent instances from behaving as expected when tested for uniqueness in Array#uniq or when used as Hash keys.
Add this line to your application's Gemfile:
And then execute:
Or install it yourself as:
$ gem install equatable
It is assumed that your objects are value objects and the only values that affect equality comparison are the ones specified by your attribute readers. Each attribute reader should be a significant field in determining objects values.
class Point include Equatable attr_reader :x, :y def initialize(x, y) @x, @y = x, y end end point_1 = Point.new(1, 1) point_2 = Point.new(1, 1) point_3 = Point.new(1, 2) point_1 == point_2 # => true point_1.hash == point_2.hash # => true point_1.eql?(point_2) # => true point_1.equal?(point_2) # => false point_1 == point_3 # => false point_1.hash == point_3.hash # => false point_1.eql?(point_3) # => false point_1.equal?(point_3) # => false point_1.inspect # => "#<Point x=1 y=1>"
It is important that the attribute readers should allow for performing deterministic computations on class instances. Therefore you should avoid specifying attributes that depend on unreliable resources like IP address that require network access.
Equatable ensures that any important property of a type holds for its subtypes. However, please note that adding an extra attribute reader to a subclass will violate the equivalence contract, namely, the superclass will be equal to the subclass but reverse won't be true. For example:
class ColorPoint < Point attr_reader :color def initialize(x, y, color) super(x, y) @color = color end end point = Point.new(1, 1) color_point = ColorPoint.new(1, 1, :red) point == color_point # => true color_point == point # => false point.hash == color_point.hash # => false point.eql?(color_point) # => false point.equal?(color_point) # => false
ColorPoint class demonstrates that extending a class with extra value property does not preserve the
- Fork it
- Create your feature branch (
git checkout -b my-new-feature)
- Commit your changes (
git commit -am 'Add some feature')
- Push to the branch (
git push origin my-new-feature)
- Create new Pull Request
Code of Conduct
Everyone interacting in the Equatable project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.
Copyright (c) 2012 Piotr Murach. See LICENSE for further details.