PHP inheritance of reflection methods [duplicate]

I'm using my own way of enums since older versions of PHP doesn't support them. My implementation of enums:

 class ModeOfTransport{
    const Land = 0;
    const Naval= 1;
    const Air= 2;
  

     function GetClassVars()
     {
         return array_keys(get_class_vars(get_class($this))); // $this
     }

     static function getConstants() {
         $oClass = new ReflectionClass(__CLASS__);
         return $oClass->getConstants();
     }

     static function getValues(){
         return ModeOfTransport::getConstants();
     }

     static function getDisplayText(int $val){
         $key=array_search($val,ModeOfTransport::getConstants());
         return $key;
     }
}

And since I'm having many other enums which feature also the same methods "getConstants()" etc. So i thought instead of repeating the same methods in every single class i can just use inheritance to apply it to all of them. But it didn't work as i expected. When i try:

class CustomEnum
{
    const aa="test";
    public static function getConstants() {
        $oClass = new ReflectionClass(self::class);
        return $oClass->getConstants();
    }

    public static function getValues(){
        return self::getConstants();
    }

    public static function getDisplayText(int $val){
        $key=array_search($val,ModeOfTransport::getConstants());
        return $key;
    }
}

    class DocumentMainType extends CustomEnum {
    const VehicleDocument = 0;
    const DriverDocument= 1;

}


//And calling the related method:
$var=DocumentMainType::getConstants();
//$var is: {"aa":"test"}
//Expected $var: {"VehicleDocument":0,"DriverDocument":1}

How can i get it to work so that those classes who inherit CustomEnum class can easily reflect their variables through inherited getConstants() method.

Thank you