controller.php

<?php

private function rules($user = null) {

    $rules = [
        'name'     => 'required|min:4',
        'email'    => 'required|email|unique:users',
        'password' => 'required|min:8'
    ];

    if ($user) {
        $rules['email']    = 'required|email|unique:users,id,'.$user['id'];
        $rules['password'] = 'sometimes|min:8';
    }

    return $rules;
}