Custom Validation Rules: Using Extensions

<?php

namespace App\Providers;

use Illuminate\Support\ServiceProvider;
use Illuminate\Support\Facades\Validator;

class AppServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap any application services.
     *
     * @return void
     */
    public function boot()
    {
        Validator::extend('foo', function ($attribute, $value, $parameters, $validator) {
            return $value == 'foo';
        });
    }

    /**
     * Register the service provider.
     *
     * @return void
     */
    public function register()
    {
        //
    }
}

Validator::extend('foo', 'FooValidator@validate');

"foo" => "Your input was invalid!",

"accepted" => "The :attribute must be accepted.",

// The rest of the validation error messages..

/**
 * Bootstrap any application services.
 *
 * @return void
 */
public function boot()
{
    Validator::extend(...);

    Validator::replacer('foo', function ($message, $attribute, $rule, $parameters) {
        return str_replace(...);
    });
}

$rules = ['name' => 'unique'];

$input = ['name' => null];

Validator::make($input, $rules)->passes(); // tru

Validator::extendImplicit('foo', function ($attribute, $value, $parameters, $validator) {
    return $value == 'foo';
});