在PHP中重載多級繼承中的函數，但沒有任何參數

Question

我正在學習PHP，剛剛開始使用中間級別。下面是類層次結構 -

FamilyTree 
    | 
    | 
Grandparents 
    | 
    | 
Parents 

Parents呼籲$dob其餘額外的屬性從Grandparents

我能超載​​，因爲它們在參數的數目不同繼承的，我怎麼超載display_values()因爲它沒有任何爭論？

這是代碼：

<?php 

class FamilyTree { 

    protected $name; 
    protected $sex; 
    protected $married; 
    protected $number_of_kids; 

    public function display_values() { 
     echo $this->name   . "<br />"; 
     echo $this->sex    . "<br />"; 
     echo $this->married   . "<br />"; 
     echo $this->number_of_kids . "<br />"; 
    } 
} 

class Grandparents extends FamilyTree { 

    public function set_values($name, $sex, $married, $number_of_kids) { 
     $this->name   = $name; 
     $this->sex   = $sex; 
     $this->married  = $married; 
     $this->number_of_kids = $number_of_kids; 
    }  
} 

class Parents extends Grandparents { 

    private $dob; 

    public function __call($function_name, $arguments) { 
     if($function_name == 'set_values' && count($arguments) == 5) { 
      $this->$name   = $name; 
      $this->sex   = $sex; 
      $this->married  = $married; 
      $this->number_of_kids = $number_of_kids; 
      $this->dob   = $dob; 
     } 
    } 
} 

$gp = new Grandparents(); 
$gp->set_values("James", "Male", 'yes', 5); 

$p = new Parents(); 
$p->set_values("Samuel", "Male", 'yes', 2, '2/5/1974'); 

$gp->display_values(); 

Answer 1

對不起，令您失望，但您在「重載」該方法時未成功。

如果你把你的執行細看如果__call：

public function __call($function_name, $arguments) { 
    if($function_name == 'set_values' && count($arguments) == 5) { 
     $this->$name   = $name; 
     $this->sex   = $sex; 
     $this->married  = $married; 
     $this->number_of_kids = $number_of_kids; 
     $this->dob   = $dob; 
    } 
} 

你會發現，

• $this->$name應該$this->name
• $name，$sex，$married，$number_of_kids和$dob是全部未定義，而應該是$arguments[0]至$arguments[4]。

但是您的__call實現根本不會被調用，因爲PHP simply discards too many arguments to user-defined functions。

你可以做的，而不是，是重寫功能，並調用父類的實現與parent::：

public function set_values($name, $sex, $married, $number_of_kids, $dob = '') { 
    parent::set_values($name, $sex, $married, $number_of_kids); 
    $this->dob = $dob; 
} 

我只是初始化$dob爲空字符串，因爲它會默認爲NULL否則。
作爲一個側面說明，如果你想提供一個新的實現，需要少參數比原來的，你也可以做到這一點與默認參數：

public function set_values($name, $sex, $married, $number_of_kids = 0) { 
    parent::set_values($name, $sex, $married, $number_of_kids); 
} 

它然後可以用任意3名爲或4個參數。

對於更復雜的組合，爲每個參數聲明新實現（爲了使其與父實現兼容）並使用func_get_args來處理或重定向呼叫。

重載display_values簡單不過，因爲參數的數量是一樣的：

public function display_values() { 
    parent::display_values(); 
    echo $this->dob . "<br />"; 
} 

所以滿，你的代碼應該是這樣的：

<?php 

class FamilyTree { 

    protected $name; 
    protected $sex; 
    protected $married; 
    protected $number_of_kids; 

    public function display_values() { 
     echo $this->name   . "<br />"; 
     echo $this->sex    . "<br />"; 
     echo $this->married   . "<br />"; 
     echo $this->number_of_kids . "<br />"; 
    } 
} 

class Grandparents extends FamilyTree { 

    public function set_values($name, $sex, $married, $number_of_kids) { 
     $this->name   = $name; 
     $this->sex   = $sex; 
     $this->married  = $married; 
     $this->number_of_kids = $number_of_kids; 
    } 
} 

class Parents extends Grandparents { 

    private $dob; 

    public function set_values($name, $sex, $married, $number_of_kids, $dob = '') { 
     parent::set_values($name, $sex, $married, $number_of_kids); 
     $this->dob = $dob; 
    } 

    public function display_values() { 
     parent::display_values(); 
     echo $this->dob . "<br />"; 
    } 
} 

$gp = new Grandparents(); 
$gp->set_values("James", "Male", 'yes', 5); 

$p = new Parents(); 
$p->set_values("Samuel", "Male", 'yes', 2, '2/5/1974'); 

$gp->display_values(); 
$p->display_values(); 

Answer 2

對於方法重載的簽名和方法名應該是相同的。沒有這兩個，它不會被視爲方法重載。在這種情況下，不是超載，而是一種單獨的方法。您可以簡單地通過此display_values（$ name，$ sex，$ married，$ number_of_kids）重載並設置所有值

Answer 3

除非我誤解你，在這種情況下，您不會通過父類中的__call重載set_values。要超載，該方法必須無法訪問。

class Parents extends Grandparents { 

private $dob; 

public function __call($function_name, $arguments) { 
    echo 'called'; 
    if($function_name == 'set_values' && count($arguments) == 5) { 
     $this->$name   = $name; 
     $this->sex   = $sex; 
     $this->married  = $married; 
     $this->number_of_kids = $number_of_kids; 
     $this->dob   = $dob; 
    } 
} 

}

這將不打印 '調出的' $ P->函數set_values（ 「塞繆爾」， 「男性」， '是'，2， '1974年2月5日'）;.

要覆蓋父方法必須是人跡罕至的方法，沒關係有關參數的數目，見下面的例子：

<?php 

class FamilyTree { 

    protected $name; 
    protected $sex; 
    protected $married; 
    protected $number_of_kids; 

    private function display_values() { 
     echo $this->name   . "<br />"; 
     echo $this->sex    . "<br />"; 
     echo $this->married   . "<br />"; 
     echo $this->number_of_kids . "<br />"; 
    } 
} 

class Grandparents extends FamilyTree { 

    private function set_values($name, $sex, $married, $number_of_kids) { 
     $this->name   = $name; 
     $this->sex   = $sex; 
     $this->married  = $married; 
     $this->number_of_kids = $number_of_kids; 
    } 

    private function drawMe($a) 
    {} 

} 

class Parents extends Grandparents { 

    private $dob; 

    public function __call($function_name, $arguments) { 
     echo 'Args: ' . count($arguments); 
     echo ' | Function name: ' . $function_name; 
     if($function_name == 'set_values' && count($arguments) == 5) { 
      $this->$name   = $name; 
      $this->sex   = $sex; 
      $this->married  = $married; 
      $this->number_of_kids = $number_of_kids; 
      $this->dob   = $dob; 
     } 
    } 
} 


$p = new Parents(); 
$p->display_values(); 
echo '<br><br>'; 
$p->set_values("Samuel", "Male", 'yes', 2, '2/5/1974'); 

此打印：

參數數量：0 |函數名稱：display_values

參數：5 |函數名稱：set_values