从同一类中的另一个类变量设置类变量 - PHP - Set class variable from another class variable within same class?

PHP - Set class variable from another class variable within same class?

我正在尝试设置一个PHP类:

class SomeClass {
    private $tags = array(
        'gen1' => array('some string', 1), 
        'gen2' => array('some string', 2), 
        'gen3' => array('some string', 3), 
        'gen4' => array('some string', 4), 
        'gen5' => array('some string', 5), 
    );
    private $otherVar = $tags['gen1'][0];
}

但是这会抛出错误:

PHP解析错误:语法错误，意外的'$tags'

切换到常用的…

private $otherVar = $this->tags['gen1'][0];

返回相同的错误:

PHP解析错误:语法错误，意外'$this'

但是在函数中访问变量是可以的:

private $otherVar;
public function someFunct() {
    $this->otherVar = $this->tags['gen1'][0];
}

如何使用先前定义的类变量来定义和初始化当前的类变量，而不需要额外的函数?

最接近的方法是将赋值放在构造函数中。例如:

class SomeClass {
    private $tags = array(
        'gen1' => array('some string', 1), 
        'gen2' => array('some string', 2), 
        'gen3' => array('some string', 3), 
        'gen4' => array('some string', 4), 
        'gen5' => array('some string', 5), 
    );
    private $otherVar;
    function __construct() {
         $this->otherVar = $this->tags['gen1'][0];
    }
    function getOtherVar() {
        return $this->otherVar;
    }
}
$sc = new SomeClass();
echo $s->getOtherVar(); // echoes some string