<?php
interface IValidator {
    public function isValid($value);
}

class StringLength implements IValidator {
    private $min = 0;
    private $max = 0;

    public function __construct($min, $max) {
        $this->min = $min;
        $this->max = $max;
    }

    public function isValid($value) {
        $length = strlen($value);
        return $length >= $this->min && $length <= $this->max;
    }
}

class MinimumInteger implements IValidator {
    private $min;

    public function __construct($min) {
        $this->min = $min;
    }

    public function isValid($value) {
        return $value>= $this->min;
    }
}

class Validator extends ArrayObject {
    private $validators = array();
    public $errors = array();

    public function validate(array $input) {
        foreach($this->validators as $propertyName => $validator) {
            $value = $input[$propertyName];

            if(!$validator->isValid($value)) {
                $this->errors[] = sprintf('%s is not valid', $propertyName);
            }
        }
    }

    public function offsetGet($name) {
        if(!$this->offsetExists($name))
            return null;

        return $this->validators[$name];
    }

    public function offsetSet($name, $validator) {
        $this->validators[$name] = $validator;
    }

    public function offsetExists($name) {
        return isset($this->validators[$name]);
    }

    public function offsetUnset($name) {
        unset($this->validators[$name]);
    }
}

$data = array(
    "name" => "yo",
    "age" => 30
);

$validator = new Validator;
$validator["name"] = new StringLength(3, 10);
$validator["age"] = new MinimumInteger(20);

if(!$validator->validate($data)) {
    var_dump($validator->errors);
}