[fpc-pascal] Are there any drawbacks to "reference to"?

[Hairy Pixels]

> On Jun 6, 2022, at 2:02 AM, Jonas Maebe via fpc-pascal <fpc-pascal at lists.freepascal.org> wrote:
> 
> On 2022-06-05 18:20, Anthony Walter via fpc-pascal wrote:
> 
>> As the "reference to" feature was recently added to fpc trunk, I'd like to ask if internally there are any penalties (performance perhaps) or drawbacks to using them in place of the more traditional "procedure" and "procedure of object" types?
> 
> The downside is that a "reference to" always gets wrapped in a reference-counted interface, and hence is much more expensive than a place procedural variable ("of object" or not).

First off I didn’t see Anthony’s original email, just like Sven says he doesn’t see mine. What’s going on here? I’m using a Gmail account because my personal domain was getting rejected for some reason, is Anthony on Gmail also? We need to get this fixed I think.

Anytime you assign to a reference it creates this interface wrapped object, even if you don’t call it. This is of course totally wasteful and in fact makes references not reliable as  a catch-all function pointer type since it comes with significant runtime overhead.

I think what the compiler needs to do is internally support a variant record type and switch to the correct function type at runtime. Something like this:

TCallback = record
  kind: byte;
  case byte of
    0: (proc: procedure);
    1: (ref: reference to procedure);
    2: (nested: procedure is nested);
    3: (obj: procedure of object);
end;

Does that sound correct? Personally what I want to see if a catch all type so I don’t need to make 4 different function aliases for each of FPCs callback types.

However as far as anonymous functions are concerned I was pleased to see that they can be can be assigned to other function pointer types so I can still use the feature in many cases.


Regards,
	Ryan Joseph