rails/rails — pull request #15862 by afeld (2014-06-22 19:17:50+00:00)
Title: Create an ActiveModel::Identity mixin

This commit moves ActiveRecord::Core#== and #hash into a module in ActiveModel. Any class can now include this mixin to have two instances be considered equal based on their `id`.

I considered making the attribute used for comparison configurable, but it seemed like a lot of complication for little gain. Sound reasonable?