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PHP5中文手册
类与对象（PHP 5）
PHP Manual

Overloading

Both method calls and member accesses can be overloaded via the __call, __get and __set methods. These methods will only be triggered when your object or inherited object doesn't contain the member or method you're trying to access. All overloading methods must not be defined as static. All overloading methods must be defined as public.

Since PHP 5.1.0 it is also possible to overload the isset() and unset() functions via the __isset and __unset methods respectively. Method __isset is called also with empty().

Member overloading

void __set ( string $name , mixed $value )
mixed __get ( string $name )
bool __isset ( string $name )
void __unset ( string $name )

Class members can be overloaded to run custom code defined in your class by defining these specially named methods. The $name parameter used is the name of the variable that should be set or retrieved. The __set() method's $value parameter specifies the value that the object should set the $name.

Note: The __set() method cannot take arguments by reference.

Example#1 overloading with __get, __set, __isset and __unset example

<?php
class Setter
{
    public $n;
    private $x = array("a" => 1, "b" => 2, "c" => 3);

    public function __get($nm)
    {
        echo "Getting [$nm]\n";

        if (isset($this->x[$nm])) {
            $r = $this->x[$nm];
            print "Returning: $r\n";
            return $r;
        } else {
            echo "Nothing!\n";
        }
    }

    public function __set($nm, $val)
    {
        echo "Setting [$nm] to $val\n";

        if (isset($this->x[$nm])) {
            $this->x[$nm] = $val;
            echo "OK!\n";
        } else {
            echo "Not OK!\n";
        }
    }

    public function __isset($nm)
    {
        echo "Checking if $nm is set\n";

        return isset($this->x[$nm]);
    }

    public function __unset($nm)
    {
        echo "Unsetting $nm\n";

        unset($this->x[$nm]);
    }
}

$foo = new Setter();
$foo->n = 1;
$foo->a = 100;
$foo->a++;
$foo->z++;

var_dump(isset($foo->a)); //true
unset($foo->a);
var_dump(isset($foo->a)); //false

// this doesn't pass through the __isset() method
// because 'n' is a public property
var_dump(isset($foo->n));

var_dump($foo);
?>

上例将输出：

Setting [a] to 100
OK!
Getting [a]
Returning: 100
Setting [a] to 101
OK!
Getting [z]
Nothing!
Setting [z] to 1
Not OK!

Checking if a is set
bool(true)
Unsetting a
Checking if a is set
bool(false)
bool(true)

object(Setter)#1 (2) {
  ["n"]=>
  int(1)
  ["x":"Setter":private]=>
  array(2) {
    ["b"]=>
    int(2)
    ["c"]=>
    int(3)
  }
}

Method overloading

mixed __call ( string $name , array $arguments )

The magic method __call() allows to capture invocation of non existing methods. That way __call() can be used to implement user defined method handling that depends on the name of the actual method being called. This is for instance useful for proxy implementations. The arguments that were passed in the function will be defined as an array in the $arguments parameter. The value returned from the __call() method will be returned to the caller of the method.

Example#2 overloading with __call example

<?php
class Caller
{
    private $x = array(1, 2, 3);

    public function __call($m, $a)
    {
        print "Method $m called:\n";
        var_dump($a);
        return $this->x;
    }
}

$foo = new Caller();
$a = $foo->test(1, "2", 3.4, true);
var_dump($a);
?>

上例将输出：


Method test called:
array(4) {
    [0]=>
    int(1)
    [1]=>
    string(1) "2"
    [2]=>
    float(3.4)
    [3]=>
    bool(true)
}
array(3) {
    [0]=>
    int(1)
    [1]=>
    int(2)
    [2]=>
    int(3)
}
类与对象（PHP 5）
PHP Manual