[fpc-devel] Proof of Concept ARC implementation

[Jonas Maebe]

On 29 Oct 2014, at 16:30, Sven Barth wrote:

> On 29.10.2014 14:23, Jonas Maebe wrote:
>>
>> Apple also supports mixing ARC and non-ARC code in Objective-C, but  
>> the
>> only way this works is by requiring the programmer to manually  
>> perform
>> the reference counting in non-ARC code. I don't think there's any  
>> quick
>> hack possible that allows you to mix them transparently without a  
>> lot of
>> pitfalls.
>
> We can of course also provide means to manually do reference  
> counting (will e.g. be necessary for TStringList if one has code  
> that abuses Objects[]...).

That's indeed only useful if you then also require that all code not  
written in non-ARC mode performs manual reference counting (like Apple  
does). Having it as "a possibility" does not solve the problem of  
unpredictability.

> Nevertheless if one mixes refcounting and non-refcounting code with  
> care (maybe we can add optional warnings/hints when passing  
> instances between ARC and non-ARC code) it should work.

Then you have to give a hint/warning for every inherited call inside a  
refcounted class that inherits from a non-reference-counted class,  
because it passes the refcounted instance "self" to non-ARC code. It  
completely destroys the concept of encapsulation that you shouldn't  
have to know, and in some cases even can't know, what methods do with  
their parameters or with self. Your code may work with one version of  
the parent class and suddenly break with the next version. Being  
careful is simply impossible with this way of working.


Jonas