PHP Nested Static Variable Access for Dependency Injection

Question

I would like to use this pattern to enable dependency injection in my code. I feel that it keeps with the play-doh nature of dynamic languages [1].

class A {
  static $FOO = 'Foo';
  function __construct() {
    $this->foo = self::$FOO::getInstance();
  }
}

A::$FOO = 'MockFoo';
$a = new A();

Unfortunately, this doesn't work and I get:

Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in [test.php] on line 6

I can create a temporary variable to trick the parser, but is there another way?

function __construct() {
  $FOO = self::$FOO;                                                                                                                                            
  $this->foo = $FOO::getInstance();
}

[1] http://weblog.jamisbuck.org/2008/11/9/legos-play-doh-and-programming

Answer 1

There is no alternative syntax to accomplish this. You need a temporary variable to trick the parser.

Answer 2

Try

$class = self::$FOO;
$this->foo = $class::getInstance();