Only scalar data (boolean,integer,float and string) can be contained in constants. It is possible to define constants as a resource,but it should be avoided,as it can cause unexpected results.

如果需要设置一组已定义的常量,请考虑创建一个类并使用class constants填充它.手册中略有修改的示例：

class MyClass
{
const constant1 = 'constant value';
const constant2 = 'constant value';
const constant3 = 'constant value';

  function showConstant1() {
    echo  self::constant1 . "\n";
  }
}

echo MyClass::constant3;

另请查看GhostDog发布的链接,这是一个很好的解决方法.