On the Laravel News site there's an article covering custom validation objects and using them in a Laravel-based application. This validation handling is added in Laravel v5.5 (upcoming as of the time of this post) to allow for easy extension of current validation rules.

Laravel 5.5 will introduce support for custom validation rule objects as an alternative to using Validator::extend for custom validation rules.

To define a custom validation rule, implement the IlluminateContractsValidationRule interface or use a Closure. The custom rule is then used directly in a validator.

They provide a few examples of defining these objects, using the "passes" and "message" methods defined in the interface. It also shows how to put them to use in a "validate" call on a request using both the object and closure versions. This new custom validation handling helps to replace some of the difficulty with the previous extension methods and makes it more flexible by allowing closures.