php - Abstract private functions

Question

The following code will have PHP unhappy that customMethod() is private. Why is this the case? Is visibility determined by where something is declared rather than defined?

If I wanted to make customMethod only visible to boilerplate code in the Template class and prevent it from being overriden, would I just alternatively make it protected and final?

Template.php:

abstract class Template() {
    abstract private function customMethod();

    public function commonMethod() {
        $this->customMethod();
    }
}

CustomA.php:

class CustomA extends Template {
    private function customMethod() {
       blah...
    }
}

Main.php

...
$object = new CustomA();
$object->commonMethod();
..

Answer 1

Abstract methods cannot be private, because by definition they must be implemented by a derived class. If you don't want it to be public, it needs to be protected, which means that it can be seen by derived classes, but nobody else.

The PHP manual on abstract classes shows you examples of using protected in this way.