On 29.10.2014 14:23, Jonas Maebe wrote:
On 27 Oct 2014, at 19:59, Sven Barth wrote:Florian has written me an idea two weeks ago regarding the "backwards compatibility" aspect (I won't argue the performance impact one ;) ): - TObject and all descendants are reference counted (please no size and performance discussion here) - in code that does not use ARC ("modeswitch arc off" - the default; or maybe better a local directive) all instance variables are considered "weak" - constructors of code that does not use ARC return with reference count = 1, otherwise reference count is initially 0 (like for interfaces and currently in my branch) - destructors also take care of this additional "pseudo" reference upon being called; thus the object is freed after the last ARC reference is gone AND (for legacy code) Free/Destroy has been called (thus when the reference count really reaches 0) With this approach there would be no change for legacy code (except for the additional refcount field per instance), as reference counting would only happen with enabled ARC directive/modeswitch (thus there could still be memory leaks for such classes). New code could take ARC into account and could be written accordingly with "weak" modifiers, etc.There's still the problem if you create an instance in ARC code, then pass it as a (e.g. const) parameter to a routine from a unit that does not use ARC and which stores it in a linked list or a local field, and later the instance goes out of scope in the ARC code (so it gets freed)...
Hmm... yes, that would indeed be a problem.
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[]...). 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.
Regards. Sven _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
