> On Feb 16, 2021, at 6:51 AM, Benito van der Zander via fpc-pascal
> <fpc-pascal@lists.freepascal.org> wrote:
>
> Interfaces are extremely slow. Virtual method calls are also slow. I have
> been using interfaces for reference counting, and have been thinking to
> replace it all with managed records because they are so slow (unfortunately
> records can also be slow because fpc does not always keep them in registers
> even if they are pointer sized)
It's a real concern indeed. What we're proposing with a default property
doesn't need to have these impacts but the class instantiation is going to be
affected I think.
>
> There we have:
>
> * slower creation of the class, because each implemented interface adds
> another VMT reference to the class which needs to be initialized.
How bad is this? We need to make a test case we can profile. For example if you
have a game that creates 1000 classes 60 frames per second. If adding
interfaces to the classes hurts this process we may have a deal breaker.
>
> * slower method calling because of the wrapper function
You mean for fields? We can inline those I believe but it's not fun boiler
plate for sure.
>
> * extremely slow casting an interface to the class. Never cast an interface,
> better add a method to the interface returning a class reference
>
We can avoid casting using the default property but it will still be possible
to cast the class if you want to.
> * slow reference counting. Especially if it is thread safe and exception safe
> with the implicit exception block
It's a whole other topic but FPC needs opt-in ARC at the language level for
classes. Interfaces are not only slow but then you need to pass around a
reference to the interface instead of the class you actually care about. It
makes no sense to me whatsoever.
Regards,
Ryan Joseph
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