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php - PHP：成员函数无法访问成员变量

问题描述

我正在试验 PHP 类，并创建了这个简单的类：

<?php

  /* email.php

    Returns a wrapper object that handles the sending of an email

  */

  class Email 
  {
    private $message = "";
    private $subject = "";
    private $to = "";

    public function setMessage(string $newMessage) {
      $this->$message = $newMessage;
    }

    public function setSubject(string $newSubject) {
      $this->$subject = $newSubject;
    }

    public function setRecipient(string $newRecipient) {
      $this->$to = $newRecipient;
    }

    public function send() {
      mail($this->$to, $this->$subject, $this->$message);
    }
  }

  $email = new Email();
  $email->setRecipient('test@gmail.com');
  $email->setSubject('A message');
  $email->setMessage('Does this work?');
  $email->send();

?>

但是，当我运行它时（我通过前端的 fetch 请求调用此脚本），我收到以下错误：

Notice: Undefined variable: to in /home/jack/Projects/test/php/email.php on line 24

Notice: Undefined variable: subject in /home/jack/Projects/test/php/email.php on line 20

Notice: Undefined variable: message in /home/jack/Projects/test/php/email.php on line 16

Notice: Undefined variable: to in /home/jack/Projects/test/php/email.php on line 28

Notice: Undefined variable: subject in /home/jack/Projects/test/php/email.php on line 28

Notice: Undefined variable: message in /home/jack/Projects/test/php/email.php on line 28

我在这里做错了什么？

标签： phpclass

解决方案

那是因为你在做$this->$subject，你的意思是$this->subject。

更全面的答案：

PHP 允许您拥有自定义变量名称。例如你可以设置

$i = 0;

$var$i = "abc";

然后$var0将包含“abc”。

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