Validation

model.rb

class Model
  attr_accessor :title
  # has-a validator
  def validator
    @validator ||= ModelValidator.new(self)
  end
end

# Represents a validation attempt
class Validation
  attr_reader :errors
  def initialize(errors)
    @errors = errors
  end
end

require "delegate"
class Validator < SimpleDelegator
  include ActiveModel::Validations
  # @return [Validation]
  def validate
    super
    Validation.new(errors)
  end
end

class ModelValidator < Validator
  validates_presence_of :title
end