类属性声明 [英] class attribute declaration

问题描述

我没有使用PHP，但我尝试过这样的：

I didn't use PHP in a while, but I've tried something like this:

<?php

class Something {
    public $x = 2 * 3;   // (line 4)
}

此代码会触发以下错误：

This code triggers the following error:

[2013年2月13日17:43:56] [错误] [客户端127.0.0.1] PHP解析错误：语法错误，意外的'*' ，在第4行的/var/www/problem.php中预期为'，'或';'。

[Wed Feb 13 17:43:56 2013] [error] [client 127.0.0.1] PHP Parse error: syntax error, unexpected '*', expecting ',' or ';' in /var/www/problem.php on line 4

PHP文档说

这个初始化必须是一个常量值 - 也就是说，它必须能够在编译时进行求值，并且不能依赖运行时信息来进行求值。

this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

所以，根据文档，我的代码应该工作。

So, according to the docs, my code should work. Is there something I'm missing here?

推荐答案

当声明一个类的成员时，你可以给它们赋值，但你可以' t做复杂的操作，如数学或函数调用。

When declaring members of a class you can assign values to them but you can't do complex operations like math or function calls.

<?php

class Something {
    public $x = 2 * 3;   // (line 4)
}

可以是：

<?php

class Something {
    public $x = 6;   // (line 4)
}

所以在你的case你会想初始化

So in your case you'll want to initialize that value in your constructor instead.

<?php

class Something {
    public $x; 

    public function __construct() 
    {
        $this->x = 2 * 3;
    }  
}

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