PHP静态调用非静态方法的应用分析
静态调用非静态方法!!这在java,c#中是不可想象的,也是绝对不行的。这样的错误在这些语言中会在编译阶段就被指出错误的。但是对于php这样的动态语言呢?首先这个是语法没有错误的,php –l 找不出错误来的。如果运行呢?
先看一个例子
复制代码 代码如下:
class myClass
{
private $name = "myClass";
public function echoName(){
echo $this->name;
}
public function getName(){
$this->echoName();
}
}
class newClass
{
private $name = "newClass";
public function echoName(){
echo $this->name;
}
public function test() {
myClass::getName();
echo "\n";
}
}
$app = new newClass();
$app->test();
这个代码的最终调用结果是什么呢?(运行环境PHP 5.3.10 )
看这个结果,有几个地方值得注意:
首先是myClass::getName() 这是一个静态函数的调用
但是看一下myClass的getName()函数,它却并不是一个静态函数。
其次返回的结构
先是返回PHP Strict Standards Error。熟悉php的人应该知道,Strict Error是php的编码标准化警告,一般是由于php为了保持向前兼容而报出的错误。那这么说,非静态函数的静态调用在php5.3之前的某个版本是允许的,只是在后面的版本是不被建议使用!!
好了,如果你现在将Strict Error在error_reporting中注释掉,返回结果就变成了newClass!!
在php4版本的时候,子类需要调用父类的方法,但是子类又有一个同名的方法,因此不能使用$this,于是php4提供了(parentClassName::method())这样的方法。(当然php5增加了parent这个关键字)
但是php4提供的这个方法实际上就是允许了静态调用一个非静态方法!!后台由于需要向前兼容的原因,这个特性也就变成了不能删除的特性了(必须保证前面版本的代码能在后一版本的php环境中运行)。
只是增加了Strict Error来对这种调用进行提示。
底层实现原因
好了,对于为什么会出现这个情况的实现原因, 鸟哥的这篇文章有说明 http://www.laruence.com/2012/06/14/2628.html
首先需要颠覆自己的观点,什么是静态调用?并不是说有::就是静态调用,而是看calling scope。
“ $this指针指向的对象就是这个方法被调用时刻的calling scope.”
我换一种句子翻译:
静态调用是没有calling scope的,非静态调用$this->abc() 中的$this指向的对象就是calling scope。
Calling scope是当每一句调用的时候被传递的。
理解下面的代码:
复制代码 代码如下:
class A {
public function __construct() {
}
}
class B extends A {
public function __construct() {
parent::__construct();
}
}
这里的parent::_construct()是子类将calling scope转化为父类A的calling scope。这个并不是静态调用。
回到最上面的例子
myClass::getName();
这个时候由于没有使用parent这样的关键字,也没有对$this重新赋值,因此calling scope并没有改变,仍然是$app。就是说这个时候,所有出现的$this指针都是指向$app的。
好了,下面的事情就很好理解了, echo $this->name; 自然就是调用calling scope的name属性了。

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