這篇文章介紹的內容是關於【php類別與物件】物件與引用，有著一定的參考價值，現在分享給大家，有需要的朋友可以參考一下
物件與引用
PHP 的引用是別名，就是兩個不同的變數名字指向相同的內容。
在 PHP 5，一個物件變數已經不再保存整個物件的值。只是保存一個標識符來存取真正的物件內容。當物件作為參數傳遞，作為結果返回，或者賦值給另一個變量，另外一個變量跟原來的不是引用的關係，只是他們都保存著同一個標識符的拷貝，這個標識符指向同一個對象的真正內容。
Example #1 引用和对象<?phpclass A {
public $foo = 1;
}
$a = new A;$b = $a; // $a ,$b都是同一个标识符的拷贝
// ($a) = ($b) = <id>$b->foo = 2;echo $a->foo."\n";$c = new A;$d = &$c; // $c ,$d是引用
// ($c,$d) = <id>$d->foo = 2;echo $c->foo."\n";$e = new A;function foo($obj) {
// ($obj) = ($e) = <id>
$obj->foo = 2;
}
foo($e);echo $e->foo."\n";?>User Contributed Notes
/*
Notes on reference:
A reference is not a pointer. However, an object handle IS a pointer. Example:
*/<?phpclass Foo {
private static $used; private $id; public function __construct() {
$id = $used++;
} public function __clone() {
$id = $used++;
}
}$a = new Foo;
// $a is a pointer pointing to Foo object 0$b = $a;
// $b is a pointer pointing to Foo object 0, however, $b is a copy of $a$c = &$a;
// $c and $a are now references of a pointer pointing to Foo object 0$a = new Foo;
// $a and $c are now references of a pointer pointing to Foo object 1, $b is still a pointer pointing to Foo object 0unset($a);
// A reference with reference count 1 is automatically converted back to a value. Now $c is a pointer to Foo object 1$a = &$b;
// $a and $b are now references of a pointer pointing to Foo object 0$a = NULL;
// $a and $b now become a reference to NULL. Foo object 0 can be garbage collected nowunset($b);
// $b no longer exists and $a is now NULL$a = clone $c;
// $a is now a pointer to Foo object 2, $c remains a pointer to Foo object 1unset($c);
// Foo object 1 can be garbage collected now.$c = $a;
// $c and $a are pointers pointing to Foo object 2unset($a);
// Foo object 2 is still pointed by $c$a = &$c;
// Foo object 2 has 1 pointers pointing to it only, that pointer has 2 references: $a and $c;const ABC = TRUE;
if(ABC) {
$a = NULL;
// Foo object 2 can be garbage collected now because $a and $c are now a reference to the same NULL value
} else {
unset($a);
// Foo object 2 is still pointed to $c
}<?php
//The two are meant to be the same$a = "Clark Kent";
//a==Clark Kent$b = &$a;
//The two will now share the same fate.$b="Superman";
// $a=="Superman" too.echo $a;
echo $a="Clark Kent";
// $b=="Clark Kent" too.unset($b);
// $b porced from $a$b="Bizarro";
echo $a;
// $a=="Clark Kent" still, since $b is a free agent pointer now.
//The two are NOT meant to be the same.$c="King";
$d="Pretender to the Throne";echo $c."\n";
// $c=="King"echo $d."\n";
// $d=="Pretender to the Throne"swapByValue($c, $d);
echo $c."\n";
// $c=="King"echo $d."\n";
// $d=="Pretender to the Throne"swapByRef($c, $d);
echo $c."\n";
// $c=="Pretender to the Throne"echo $d."\n";
// $d=="King"function swapByValue($x, $y)
{
$temp=$x;$x=$y;$y=$temp;
//All this beautiful work will disappear
//because it was done on COPIES of pointers.
//The originals pointers still point as they did.}function swapByRef(&$x, &$y)
{
$temp=$x;$x=$y;
$y=$temp;
//Note the parameter list: now we switched 'em REAL good.
}
?>相關推薦：
#以上是【php類別與物件】物件與引用的詳細內容。更多資訊請關注PHP中文網其他相關文章！
