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Subject: Re: [PHP-DEV] weak references
From: lars.schultz@toolpark.com (Lars Schultz)

Am 17.07.2011 17:40, schrieb Hannes Landeholm:
> If you are writing code that caches objects/relations and that caching has a
> significant impact on memory usage, you need to care about memory
> allocation/management per definition.
Right. That's what I am talking about...a callback on high-memory 
consumption and a way to check which objects I could liberate from my cache.

> So then you have to learn how OOP
> memory managment works (which should be obligatory anyway if you want to
> call yourself a OOP-developer IMO).
I do call myself an OOP-developer but maybe I shouldn't, because I've 
never heard of "OOP Memory Management". Would you care to explain in 
private?

> A common argument to why programmers
> should not start with a garbage collected language is that it prevents them
> from understanding memory allocation concepts.
The other argument being that if you're not using a gc-language, it 
might prevent you from starting at all.

> It would probably be simple to implement such functionality. However this
> would be bad design since it would violate responsibility isolation. PHP
> should expose as little internal stuff to the userland as possible - unless
> there are a clear use case for it, and even then it might be a bad idea
> because it could cause BC breaks in future updates.

I agree with you that it's not an ideal solution. But my solution would 
not introduce a completely new concept to the language, but would allow 
advanced PHP-users to write their own custom bred solution. => "give the 
language a rest"

> If you write code that
> depend on reference counts or memory usage - you're doing something wrong.
Why?...because it's not discrete? I am only taking advantage of what is 
already there...

> The only scenario I could imagine where you could "free memory"
> spontaneously on demand (when the arbitrary OOM limit is reached) - is if
> that would be cached data.
Exactly the case I wanted to cover.

> Caching is a very complicated subject that is not
> directly related to weak references. Start a separate thread about it and
> present clear use cases if you have anything special in mind.
I know but WeakReferences (or SoftReferences) would be a solution to 
this, right? It's not unrelated.

> For example, I need weak references to store a table of "back references"
> between objects for later reference (depends on how you use the objects). If
> A references B i also need a weak reference from B to A so if B should be
> replaced with a C object I need the weak reference from B to A to know that
> A should be updated to point to C instead (if A still exists). This is not
> related to caching.

I am looking forward to the RFCs usecases...this sounds interesting.