如何创建具有可选参数的构造函数

1. PHP中没有重载；不能有名称相同但参数不同的方法

2. 由于您的所有属性都将默认为null，因此没有理由自己这样做。我建议做以下事情：

   public function __construct($nick = null) {
       if ($nick != null) {
           $query = "SELECT * FROM Users WHERE nick='".$nick."'";
           $result = App::runQuery($query);
           $user = $result->fetch_object();
           $this->id = $user->id;
           $this->nick = $user->nick;
           $this->email = $user->email;
           $this->password = $user->password;
           $this->birthDay = $user->birthDay;
           $this->sex = $user->sex;
           $this->about = $user->about;
           $this->city = $user->city;
           $this->photo = $user->photo;
           $this->following = $user->following;
           $this->followers = $user->followers;
           $this->statu = $user->statu; 
       }
   }
   

3. 上面代码的一个替代方案是拥有多个静态构造函数方法，并使用一个私有构造函数：

   private function __construct() {
   }
   public static function createFromNick($nick) {
       $self = new self();
       $query = "SELECT * FROM Users WHERE nick='".$nick."'";
       $result = App::runQuery($query);
       $user = $result->fetch_object();
       $self->id = $user->id;
       $self->nick = $user->nick;
       $self->email = $user->email;
       $self->password = $user->password;
       $self->birthDay = $user->birthDay;
       $self->sex = $user->sex;
       $self->about = $user->about;
       $self->city = $user->city;
       $self->photo = $user->photo;
       $self->following = $user->following;
       $self->followers = $user->followers;
       $self->statu = $user->statu;
       return $self;
   }
   public static function createEmpty() {
       return new self();
   }
   

public function __construct() {
    // allocate your stuff
}
public static function withRow( array $row ) {
    $instance = new self();
    $instance->fill( $row );
    return $instance;
}
protected function fill( array $row ) {
    // fill all properties from array
}

有关详细信息，请查看以下答案：在PHP 中执行多个构造函数的最佳方法

非常感谢您的回答。我已经用自己的方法解决了这个问题。

public function __construct($nick) {
    if($nick != NULL) {//for user 
        $query = "SELECT * FROM Users WHERE nick='".$nick."'";
        $result = App::runQuery($query);
        $user = $result->fetch_object();
        $this->id = $user->id;
        $this->nick = $user->nick;
        $this->email = $user->email;
        $this->password = $user->password;
        $this->birthDay = $user->birthDay;
        $this->sex = $user->sex;
        $this->about = $user->about;
        $this->city = $user->city;
        $this->photo = $user->photo;
        $this->following = $user->following;
        $this->followers = $user->followers;
        $this->statu = $user->statu; 
    }else {//for null
        $this->id = NULL;
        $this->nick = NULL;
        $this->email = NULL;
        $this->password = NULL;
        $this->birthDay = NULL;
        $this->sex = NULL;
        $this->about = NULL;
        $this->city = NULL;
        $this->photo = NULL;
        $this->following = NULL;
        $this->followers = NULL;
        $this->statu = NULL;
    }
}

它有效！