PHP:在静态变量中引用另一个静态变量

Question

要么我太笨，要么这在 php 中是不可能的(这实际上是任何编程语言中的基本功能......):
所以这是我的问题的例子:

class Test {
 private static $A = "test";
 private static $B = "This is a " . Test::$A . " to see if it works";
}

我的预期结果是变量 $B具有值 = This is a test to see if it works
但不知何故我收到了这个错误:

Parse error: syntax error, unexpected '$A' (T_VARIABLE), expecting identifier (T_STRING) or class (T_CLASS) in /.../class.Test.php on line 4

这是什么东西 php是无法做到还是只是一些愚蠢的错字？大约一个小时后，我无法找到错误...

提前致谢

Answer 1

如果你不想有另一个类(class)，另一种解决方案

class TestStatic
{
    private static $A = 'test';
    private static $B;

    //if you want to instantiate the object
    public function __construct() {
        self::setB();
    }

    //if you don't want to instantiate the class 
    public static function getB() {
        self::setB();
       return self::$B;
    }

    private static function setB() {
       if (!isset(self::$B)) {
        self::$B = 'This is a '.self::$A.' to see if it works';
    }
}

}

echo TestStatic::getB();