PHP7 - class static variable doesn't support variable function

Question

In PHP7.4.3, I'm trying to use class static variable to refer to different class static member functions as below:

1  class ColorT {
2    static $color = "yellow";
3    static function yellow() {
4        echo "yellow"."<br>";
5    }
6    static function green() {
7        echo "green"."<br>";
8    }
9  }

10 ColorT::$color();  //ColorT::yellow() function is expected to be called

11 $global_color = "yellow";
12 ColorT::$global_color();  //ColorT::yellow() function is expected to be called

Both line 10 and line 12, I expect ColorT::yellow() to be invoked.
Line 12 works as expected.
But in line 10, it print error :

PHP Fatal error: Uncaught Error: Function name must be a string

Doesn't php support class static variable referring to class static member functions?
If it's supported, then how to fix the error mentioned in line 10?

Answer 1

In line 10, ColorT::$color is "yellow". So ColorT::$color() would call yellow(), not ColorT::yellow().

You could use the callbable ['ColorT', ColorT::$color] for this, to call ColorT::yellow(), dynamically.

Example :

class ColorT {
  static $color = "yellow";
  static function yellow() {
      echo "yellow"."<br>";
  }
  static function green() {
      echo "green"."<br>";
  }
}

$method = ['ColorT', ColorT::$color];
$method();

Output :

yellow<br>

---

Another way is to create a method in ColorT :

static public function callFunc() 
{
    [__class__, self::$color]();
}

and use

ColorT::callFunc(); // "yellow<br>"

You can also check using is_callable()