Php 在抽象类中声明的方法中从子级重写Get常量

我有这个（缩短）：

问题是，$c:：DBID/TOKEN在php<5.3中不起作用

是否有一种方法可以从与5.2.9兼容的抽象类中完成相同的任务？

编辑： 常数并不真正意味着要在对象实例化过程中被改变，您可能需要考虑成员变量。 抽象类不能直接实例化。您可以创建一个子类来扩展抽象类，然后调用getDb（）

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我在PHP5.2代码库中有一个解决方案，它使用反射从超类中获取子类的常量，但我建议不要这样做，除非这是绝对必要的，因为反射在PHP中是性能相对昂贵的工具

PHP5.3引入了static:：CONST中的static关键字，而不是self:：CONST来访问类的静态成员。我从未真正尝试过，但我相信它应该能够满足你的需要。在PHP手册中查找最新的静态绑定

下面是一个使用反射来获取子类常量的方法的代码

class SomeClass
{
    /**
     * Get reflection class for item
     * 
     * Get a reflector for this item so that internal constants can be used for the permission checking
     * functions.  This is necessary because of how static binding works prior to PHP 5.3.  
     * 
     * @return ReflectionClass
     */
    protected function getRef ()
    {
        if (!$this -> ref)
        {
            $this -> ref    = new ReflectionClass ($this);
        }
        return ($this -> ref);
    }

    /**
     * Check that the user has permission to create an item of the type this object represents
     *
     * @todo Use late static binding instead of reflection once PHP 5.3 becomes available on the server
     * @return bool True if OK
     */
    public function canCreate ()
    {
        $ref    = $this -> getRef ();
        if ($flag = $ref -> getConstant ('USR_FLAG_CREATE'))
        {
            return (self::$user -> permissions [$flag]);
        }
    }
}

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在抽象构造函数中，我不会这样做：$this->setDbId（父：：$dbID）和$this->setToken（父：：$token）？如果要使用相同值的父版本，只需取出子版本的重写值，那么对getDb（）的任何调用都将使用父版本。我只是向您展示了此解决方案提供的灵活性。

abstract class MyModel
{
    private $dbId;
    private $token;

    public function setDbId($dbId)
    {
        $this->dbId = $dbId;
    }

    public function setToken($token)
    {
        $this->token = $token;
    }

    public function getDbId()
    {
        return $this->dbId;
    }

    public function getToken()
    {
        return $this->token;
    }

    public function __construct()
    {
        // All child classes will have the same values
        $this->setDbId('myParentDbId');
        $this->setToken('myParentToken');
    }

    protected function getDb()
    {
        echo $this->getDbId();
        echo $this->getToken();
    }
}

class MyChildModel extends MyModel
{
    // Don't need any methods, just access to abstract parent
    // But if I wanted to override my parent I could do this
    public function __construct()
    {            
        parent::__construct();

        $this->setDbId('myChildDbId');
        $this->setToken('myChildToken');
    }
}

$myChildModel = new MyChildModel();
var_dump($myChildModel->getDb());

class SomeClass
{
    /**
     * Get reflection class for item
     * 
     * Get a reflector for this item so that internal constants can be used for the permission checking
     * functions.  This is necessary because of how static binding works prior to PHP 5.3.  
     * 
     * @return ReflectionClass
     */
    protected function getRef ()
    {
        if (!$this -> ref)
        {
            $this -> ref    = new ReflectionClass ($this);
        }
        return ($this -> ref);
    }

    /**
     * Check that the user has permission to create an item of the type this object represents
     *
     * @todo Use late static binding instead of reflection once PHP 5.3 becomes available on the server
     * @return bool True if OK
     */
    public function canCreate ()
    {
        $ref    = $this -> getRef ();
        if ($flag = $ref -> getConstant ('USR_FLAG_CREATE'))
        {
            return (self::$user -> permissions [$flag]);
        }
    }
}