Using self closes the possibility of class extension.

[razvan-tache]

By having all methods static, and using self, the possibility of extending functionality / replacing small parts disappears.

eg.

If I want to replace the following verifyResponse method to act differently, I can't, as the call will always be called on the self context (in the class used).

$result = self::verifyResponse(OpenPayU_Http::doPost($pathUrl, $data, $authType), 'RefundCreateResponse');

The self keyword can be replaces with the static keyword, which will use the static context of the object.

$result = static::verifyResponse(OpenPayU_Http::doPost($pathUrl, $data, $authType), 'RefundCreateResponse');

In this way, I can create a new class MyRefund which extends the refund functionality, but on verify response does something else.