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Date: Thu, 23 May 2013 16:24:45 -0500
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Subject: Cannot call constructor
From: ceo@l-i-e.com ("Richard Lynch")

Consider this common scenario:

I use some OOP library, that is a "black box" and I like it that way.

As part of the integration, I need to extend one of the library's
classes:

class App_bar extends Library_foo{
  function __construct(){
    //do whatever I need to do here.
  }
}

So I write this code, and it works, and I'm happy.

Years go by and new releases of the library come out, steadily
improving features and fixing bugs etc.

But at some point, the library needed a resource in a __construct()
somewhere in the ancestry of Library_foo, to perform something at the
time of construction.

So they re-factored or re-implemented the black box library to have a
constructor in Library_foo class, or any of its numerous ancestors.

Suddenly my code doesn't work. Maybe the resource is only needed under
certain conditions. So their __construct doesn't get called, but
nothing bad happens until the circumstances where they need the
__construct called.

So now I don't just have a bug, I have an intermittent bug.

And as much as we all like to think our testing covers 100% of the
functionality...

I'm tearing my hair out trying to find where things went wrong in code
that worked for years.

Right now, to avoid this situation, you have to do:
if (method_exists(get_parent_class(), '__construct'))
parent::__construct();

If you don't check for the method existing, you get:
Fatal error: Cannot call constructor ...

I don't want to have an intimate knowledge of the internals of the
library; just the documented API. That's one of the major reasons for
using a library.

I would think that as PHP climbs up the chain of "extends" et al, if
it never found a parent method, if wouldn't complain about it, much
less E_FATAL...

I mean, so you didn't find a method that's not there to find. And I
should call parent::__construct just in case there is one there,
because I don't know, or care, really, how the black box is
implemented. So long as the library does what's on the tin (in the
docs).