Chris wrote:
This gives the problem away..
http://www.php.net/manual/en/language.oop5.abstract.php
Any class that contains at least one abstract method must also be
abstract.
Make 'A' abstract:
abstract class A
Sorry for the poor example. I did catch that after submitting my post,
but it didn't really matter. Adding abstract to the class doesn't solve
the problem. Here I do as you say and still get the error:
---------- 8< -------------------- 8< -------------------- 8< ----------
<?php
// Change to E_ALL for development/debugging
error_reporting(E_ALL | E_NOTICE);
ini_set('display_errors', 'On');
// defines base functions and requires derived classe to replace foo()
abstract class A {
protected abstract function foo();
public static function bar() {
print __CLASS__;
$x = new self();
$x->foo();
}
}
// defines foo() as it should, but base class doesn't know foo exists
// when it references self()
class B extends A {
protected function foo() {
echo "hello world";
}
}
// show how broken things are
B :: bar();
?>
---------- 8< -------------------- 8< -------------------- 8< ----------
Output:
A
*Fatal error*: Cannot instantiate abstract class A in *.../demo.php* on
line *11
The problem is that when method bar() is invoked on class B statically,
class B is complete ignored. Since bar() is only defined inside class
A, the B :: bar() call seems to be translated into a call of A::bar()
and class B is no longer addressable.
My expectation is that when I call an object, the search for a method or
property should start at the bottom-most derived object and work it's
way up the dependency tree. This doesn't happen, though. It appears
that any class can only reference base class and inherited methods and
never derived methods. Perhaps this is only symptomatic when referenced
statically?
Dante
*
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