【PHP趣味】new self和new static的区别

<?php

class Test {
private $_user;
protected function __construct($user) {
$this->_user = $user;
}
public function showUser() {
echo "{$this->_user}\n";
}
public static function of($user) {
return new static($user);
}
}

class MyTest extends Test {
protected function __construct($user) {
parent::__construct('from MyTest: '.$user);
}

}

class Test2 {
private $_user;
protected function __construct($user) {
$this->_user = $user;
}

public function showUser() {
echo "{$this->_user}\n";
}

public static function of($user) {
return new self($user);
}
}

class MyTest2 extends Test2 {
protected function __construct($user) {
parent::__construct('from MyTest: '.$user);
}
}

MyTest::of("hello world")->showUser();
MyTest2::of("hello world")->showUser();

输出结果：

from MyTest: hello world

hello world

小结：

一般情况下new self就是实例化这行代码所在的类，但如果是子类调用父类的方法（如上面父类的of），在这个父类方法里实例化子类，就可以new static来实现（换句话说new static实现了在父类里实例化子类），这也是多态的体现，让程序更加灵活。（在YII框架中有应用）