php - 覆盖静态变量

Question

我有两个类(模型和用户)但是我有一个问题所以我试着用一个简单的例子来解释它:

class person
{
    protected static $todo ="nothing";

    public function __construct(){}

    public function get_what_todo()
    {
        echo self::$todo;
    }
}

class student extends person
{
    protected static $todo ="studing";
}

$s = new student();
$s->get_what_todo(); // this will show the word (nothing)
                     //but I want to show the word (studing)

请给我一个解决方案，但我不想在学生类(class)写任何函数，我只想在那里做声明 :) 谢谢 :)

Answer 1

原理称为“late static binding”，在 PHP 5.3.0 中引入；使用 self 关键字访问继承树中调用类中定义的属性，或使用 static 访问继承树中子类中定义的属性。

class person
{
    protected static $todo ="nothing";

    public function __construct(){}

    public function get_what_todo()
    {
        echo static::$todo;  // change self:: to static::
    }
}

class student extends person
{
    protected static $todo ="studying";
}

class teacher extends person
{
    protected static $todo ="marking";
}

class guest extends person
{
}

$s = new student();
$s->get_what_todo(); // this will show the "studying" from the instantiated child class

$t = new teacher();
$t->get_what_todo(); // this will show the "marking" from the instantiated child class

$g = new guest();
$g->get_what_todo(); // this will show the "nothing" from the parent class,
                     // because $todo is not overriden in the child class