required if validation in laravel example

Example 1: laravel required if

"sale_price" => "required_if:list_type,==,selling"

Example 2: laravel validation

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

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