你不能在一个PHP类中放入两个具有唯一参数签名的__construct函数。我想这样做:

class Student 
{
   protected $id;
   protected $name;
   // etc.

   public function __construct($id){
       $this->id = $id;
      // other members are still uninitialized
   }

   public function __construct($row_from_database){
       $this->id = $row_from_database->id;
       $this->name = $row_from_database->name;
       // etc.
   }
}

PHP中最好的方法是什么?


当前回答

PHP是一种动态语言,因此不能重载方法。你必须像这样检查参数的类型:

class Student 
{
   protected $id;
   protected $name;
   // etc.

   public function __construct($idOrRow){
    if(is_int($idOrRow))
    {
        $this->id = $idOrRow;
        // other members are still uninitialized
    }
    else if(is_array($idOrRow))
    {
       $this->id = $idOrRow->id;
       $this->name = $idOrRow->name;
       // etc.  
    }
}

其他回答

Kris的回答很好,但正如Buttle Butku评论的那样,新的static()将在PHP 5.3+中被首选。

所以我会这样做(根据克里斯的回答修改):

<?php

class Student
{
    public function __construct() {
        // allocate your stuff
    }

    public static function withID( $id ) {
        $instance = new static();
        $instance->loadByID( $id );
        return $instance;
    }

    public static function withRow( array $row ) {
        $instance = new static();
        $instance->fill( $row );
        return $instance;
    }

    protected function loadByID( $id ) {
        // do query
        $row = my_awesome_db_access_stuff( $id );
        $this->fill( $row );
    }

    protected function fill( array $row ) {
        // fill all properties from array
    }
}

?>

用法:

<?php

$student1 = Student::withID($id);
$student2 = Student::withRow($row);

?>

我还在php.net OOP文档中找到了一个有用的例子。

在创建具有不同签名的多个构造函数时,我也面临着同样的问题,但不幸的是,PHP没有提供直接的方法来这样做。然而,我发现了一个技巧来克服它。希望也适用于你们所有人。

    <?PHP

    class Animal
    {

      public function __construct()
      {
        $arguments = func_get_args();
        $numberOfArguments = func_num_args();

        if (method_exists($this, $function = '__construct'.$numberOfArguments)) {
            call_user_func_array(array($this, $function), $arguments);
        }
    }
   
    public function __construct1($a1)
    {
        echo('__construct with 1 param called: '.$a1.PHP_EOL);
    }
   
    public function __construct2($a1, $a2)
    {
        echo('__construct with 2 params called: '.$a1.','.$a2.PHP_EOL);
    }
   
    public function __construct3($a1, $a2, $a3)
    {
        echo('__construct with 3 params called: '.$a1.','.$a2.','.$a3.PHP_EOL);
    }
}

$o = new Animal('sheep');
$o = new Animal('sheep','cat');
$o = new Animal('sheep','cat','dog');

// __construct with 1 param called: sheep
// __construct with 2 params called: sheep,cat
// __construct with 3 params called: sheep,cat,dog

让我在这里加一粒沙子

我个人喜欢将构造函数作为返回类(对象)实例的静态函数添加。代码示例如下:

 class Person
 {
     private $name;
     private $email;

     public static function withName($name)
     {
         $person = new Person();
         $person->name = $name;

         return $person;
     }

     public static function withEmail($email)
     {
         $person = new Person();
         $person->email = $email;

         return $person;
     }
 }

注意,现在你可以像这样创建Person类的实例:

$person1 = Person::withName('Example');
$person2 = Person::withEmail('yo@mi_email.com');

我的代码来自:

http://alfonsojimenez.com/post/30377422731/multiple-constructors-in-php

另一种选择是像这样在构造函数中使用默认参数

class Student {

    private $id;
    private $name;
    //...

    public function __construct($id, $row=array()) {
        $this->id = $id;
        foreach($row as $key => $value) $this->$key = $value;
    }
}

这意味着你需要实例化一行像这样:$student = new student ($row['id'], $row),但保持你的构造函数漂亮和干净。

另一方面,如果你想利用多态性,那么你可以创建两个类,像这样:

class Student {

    public function __construct($row) {
         foreach($row as $key => $value) $this->$key = $value;
    }
}

class EmptyStudent extends Student {

    public function __construct($id) {
        parent::__construct(array('id' => $id));
    }
}

嗯,很惊讶我还没有看到这个答案,假设我要参加竞选。

class Action {
    const cancelable    =   0;
    const target        =   1
    const type          =   2;

    public $cancelable;
    public $target;
    public $type;


    __construct( $opt = [] ){

        $this->cancelable   = isset($opt[cancelable]) ? $opt[cancelable] : true;
        $this->target       = isset($opt[target]) ?     $opt[target] : NULL;
        $this->type         = isset($opt[type]) ?       $opt[type] : 'action';

    }
}


$myAction = new Action( [
    Action::cancelable => false,
    Action::type => 'spin',
    .
    .
    .
]);

您可以选择将这些选项分离到它们自己的类中,例如扩展脾。

abstract class ActionOpt extends SplEnum{
    const cancelable    =   0;
    const target        =   1
    const type          =   2;
}