php三种操作符 -＞ :: =＞的区别

左手的ㄟ右手 2022-08-30 11:45 189阅读 0赞

### 文章目录 ###

*   *  来源
     *  1 箭头->与双冒号::的区别
     *   *  例子
         *  输出
     *  2 \`=>\`运算符用于在关联数组中分配键值对

## 来源 ##

[whats-the-difference-between-double-colon-and-arrow-in-php][]

## 1 箭头->与双冒号::的区别 ##

当左侧部分是**对象实例**时，使用`->`。  
否则，使用`::`。

`->`主要用于访问实例成员（虽然它也可以用于访问静态成员，但不鼓励这种用法）  
`::`通常用于访问静态成员（尽管在少数特殊情况下，它用于访问实例成员）。

通常，`::`用于[作用域解析][Link 1]，它的左边可能有一个类名`parent`、`self`、 或（在 PHP 5.3 中）`static`。  
`parent`指使用它的类的父类的范围；`self`指的是使用它的类的范围；`static`指的是“被调用的范围”（参见[后期静态绑定][Link 2]）。

当且仅当以下情况调用，用`::`是实例调用：

*  目标方法未声明为静态方法，*并且*
 *  在调用时有一个兼容的对象上下文，这意味着以下条件必须满足：
    
    1.  调用是从`$this`存在的上下文中进行的，并且
    2.  `$this`的类要么是被调用方法的类，要么是它的子类。

### 例子 ###

class A { 
        public function func_instance() { 
            echo "in ", __METHOD__, "\n";
        }
        public function callDynamic() { 
            echo "in ", __METHOD__, "\n";
            B::dyn();
        }
    
    }
    
    class B extends A { 
        public static $prop_static = 'B::$prop_static value';
        public $prop_instance = 'B::$prop_instance value';
    
        public function func_instance() { 
            echo "in ", __METHOD__, "\n";
            /* this is one exception where :: is required to access an * instance member. * The super implementation of func_instance is being * accessed here */
            parent::func_instance();
            A::func_instance(); //same as the statement above
        }
    
        public static function func_static() { 
            echo "in ", __METHOD__, "\n";
        }
    
        public function __call($name, $arguments) { 
            echo "in dynamic $name (__call)", "\n";
        }
    
        public static function __callStatic($name, $arguments) { 
            echo "in dynamic $name (__callStatic)", "\n";
        }
    
    }
    
    echo 'B::$prop_static: ', B::$prop_static, "\n";
    echo 'B::func_static(): ', B::func_static(), "\n";
    $a = new A;
    $b = new B;
    echo '$b->prop_instance: ', $b->prop_instance, "\n";
    //not recommended (static method called as instance method):
    echo '$b->func_static(): ', $b->func_static(), "\n";
    
    echo '$b->func_instance():', "\n", $b->func_instance(), "\n";
    
    /* This is more tricky * in the first case, a static call is made because $this is an * instance of A, so B::dyn() is a method of an incompatible class */
    echo '$a->dyn():', "\n", $a->callDynamic(), "\n";
    /* in this case, an instance call is made because $this is an * instance of B (despite the fact we are in a method of A), so * B::dyn() is a method of a compatible class (namely, it's the * same class as the object's) */
    echo '$b->dyn():', "\n", $b->callDynamic(), "\n";

### 输出 ###

B::$prop_static: B::$prop_static value
    B::func_static(): in B::func_static
    
    $b->prop_instance: B::$prop_instance value
    $b->func_static(): in B::func_static
    
    $b->func_instance():
    in B::func_instance
    in A::func_instance
    in A::func_instance
    
    $a->dyn():
    in A::callDynamic
    in dynamic dyn (__callStatic)
    
    $b->dyn():
    in A::callDynamic
    in dynamic dyn (__call)

## 2 `=>`运算符用于在关联数组中分配键值对 ##

$fruits = array(
      'Apple'  => 'Red',
      'Banana' => 'Yellow'
    );

在`foreach`声明中，用法是相似的

foreach ($fruits as $fruit => $color)
      echo "$fruit is $color in color.\n";

[whats-the-difference-between-double-colon-and-arrow-in-php]: https://stackoverflow.com/questions/3173501/whats-the-difference-between-double-colon-and-arrow-in-php
[Link 1]: http://www.php.net/manual/en/language.oop5.paamayim-nekudotayim.php
[Link 2]: http://www.php.net/manual/en/language.oop5.late-static-bindings.php