StandaloneValidator

require 'standalone_validator'

class NameLengthValidator < StandaloneValidator
  def initialize(min_length, attribute_name = :name)
    @min_length = min_length
    @attribute_name = attribute_name
  end

  include_validation do |object, result|
    if object.send(attribute_name).length < @min_length
      result.add_violation(attribute_name, 'should be bigger')
    end
  end

private

  attr_reader :attribute_name
end

class AllNamesValidator < StandaloneValidator
  include_validation NameLengthValidator, 5
  include_validation NameLengthValidator, 4, :last_name
end


Person = Struct.new(:name, :last_name)
validator = AllNamesValidator.new

person = Person.new("Renato", "Zannon")
puts validator.violations_of(person).any? # false

other_person = Person.new("Renato", "Foo")
puts validator.violations_of(other_person).any? # true

validator.violations_of(other_person).each do |violation|
  puts violation.attribute.inspect # :last_name
  puts violation.message.inspect   # "should be bigger"
end