C，Java和甚至Ruby(和可能的其他編程語言)允許嵌套/內部類在主類中，允許使代碼更面向對象和組織，在PHP中，我想做一些這樣的事情：
<?php
public class User {
public $userid;
public $username;
private $password;
public class UserProfile {
// Some code here
}
private class UserHistory {
// Some code here
}
}?>這是可能在PHP嗎？我該如何實現呢？如果這是不可能的，未來的PHP版本可能支持嵌套類？
嵌套類與其他類相關，有別於外部類。以Java爲例：
非靜態嵌套類可以訪問包含類的其他成員，即使它們被聲明爲私有。另外，非靜態嵌套類需要實例化父類的實例。
OuterClass outerObj = new OuterClass(arguments); outerObj.InnerClass innerObj = outerObj.new InnerClass(arguments);
使用它們有幾個令人信服的理由：
>這是一種邏輯分組只在一個地方使用的類的方法。
If a class is useful to only one other class, then it is logical to
relate and embed it in that class and keep the two together.
>它增加封裝。
Consider two top-level classes, A and B, where B needs access to
members of A that would otherwise be declared private. By hiding class
B within class A, A’s members can be declared private and B can access
them. In addition, B itself can be hidden from the outside world.
>嵌套類可以導致更可讀和可維護的代碼。
A nested class usually relates to it’s parent class and together form a “package”
在PHP中，你可以在沒有嵌套類的PHP中有類似的行爲。
如果所有你想實現的是結構/組織，如Package.OuterClass.InnerClass，PHP命名空間可能sufice。你甚至可以在同一個文件中聲明多個命名空間(雖然，由於標準的自動加載功能，這可能不可取)。
namespace;
class OuterClass {}
namespace OuterClass;
class InnerClass {}如果你想模仿其他特性，如成員可見性，需要更多的努力。
定義“包”類
namespace {
class Package {
/* protect constructor so that objects can't be instantiated from outside
* Since all classes inherit from Package class, they can instantiate eachother
* simulating protected InnerClasses
*/
protected function __construct() {}
/* This magic method is called everytime an inaccessible method is called
* (either by visibility contrains or it doesn't exist)
* Here we are simulating shared protected methods across "package" classes
* This method is inherited by all child classes of Package
*/
public function __call($method, $args) {
//class name
$class = get_class($this);
/* we check if a method exists, if not we throw an exception
* similar to the default error
*/
if (method_exists($this, $method)) {
/* The method exists so now we want to know if the
* caller is a child of our Package class. If not we throw an exception
* Note: This is a kind of a dirty way of finding out who's
* calling the method by using debug_backtrace and reflection
*/
$trace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 3);
if (isset($trace[2])) {
$ref = new ReflectionClass($trace[2]['class']);
if ($ref->isSubclassOf(__CLASS__)) {
return $this->$method($args);
}
}
throw new \Exception("Call to private method $class::$method()");
} else {
throw new \Exception("Call to undefined method $class::$method()");
}
}
}}用例
namespace Package {
class MyParent extends \Package {
public $publicChild;
protected $protectedChild;
public function __construct() {
//instantiate public child inside parent
$this->publicChild = new \Package\MyParent\PublicChild();
//instantiate protected child inside parent
$this->protectedChild = new \Package\MyParent\ProtectedChild();
}
public function test() {
echo "Call from parent -> ";
$this->publicChild->protectedMethod();
$this->protectedChild->protectedMethod();
echo "<br>Siblings<br>";
$this->publicChild->callSibling($this->protectedChild);
}
}}namespace Package\MyParent{
class PublicChild extends \Package {
//Makes the constructor public, hence callable from outside
public function __construct() {}
protected function protectedMethod() {
echo "I'm ".get_class($this)." protected method<br>";
}
protected function callSibling($sibling) {
echo "Call from " . get_class($this) . " -> ";
$sibling->protectedMethod();
}
}
class ProtectedChild extends \Package {
protected function protectedMethod() {
echo "I'm ".get_class($this)." protected method<br>";
}
protected function callSibling($sibling) {
echo "Call from " . get_class($this) . " -> ";
$sibling->protectedMethod();
}
}}測試
$parent = new Package\MyParent(); $parent->test(); $pubChild = new Package\MyParent\PublicChild();//create new public child (possible) $protChild = new Package\MyParent\ProtectedChild(); //create new protected child (ERROR)
輸出：
Call from parent -> I'm Package protected method I'm Package protected method Siblings Call from Package -> I'm Package protected method Fatal error: Call to protected Package::__construct() from invalid context
注意：
我真的不認爲試圖在PHP中模仿innerClasses是一個好主意。我認爲代碼不那麼幹淨，可讀。此外，可能有其他方法使用一個良好建立的模式，如觀察者，裝飾者ou組織模式實現類似的結果。有時，即使簡單的繼承也是足夠的。