$_POST  = [
    'email' => 'xxxx',
    'age'   => 2
];
$vt     = new Validator();
$result = $vt->validate($_POST, [
    'name'  => 'required|min_len:5|max_len:10', // required 5<= strlen(name) <=10
    'email' => 'required|email', // required email
    'age'   => 'uint|min:18|max:200'  // options Positive integer 18<= age <=200
])->isOk();

if ($result === false) {
    print_r($vt->getErrs());
}


//Array
//(
//    [0] => name can not be empty
//    [1] => email incorrect format
//    [2] => age not less than 18
//)

$vt->addRule('between', [
    'msg' => ':attribute can only be between :arg1-:arg2',
    'fn'  => function ($value, $arg1, $arg2) {
        return $value >= $arg1 && $value <= $arg2;
    }
]);

$vt->validate(['a' => 10], [
    'a' => 'required|between:3,10'
]);

// Check whether a value exists in the database
$vt->addRule('exist', [
    'msg' => 'the :attribute already exists',
    'fn'  => function ($value, $table, $filed) {
        return Model::from($table)->where($filed,$value)->find() !== null;
    }
]);

$vt->validate(['email' => 'sss@ss.com'], [
    'email' => 'required|exist:users,email'
]);