[fpc-pascal] Passing nested procs out?
Is passing nested procs outside of the calling scope relying on undefined
behavior? It doesn’t seem like this should be allowed.
===
{$modeswitch nestedprocvars}
program test;
type
TCallback = procedure (i: integer) is nested;
function DoTest: TCallback;
var
context: integer = 0;
procedure Process(x: integer);
begin
context += x;
writeln(x,' ',context);
end;
begin
result := @Process;
end;
var
c: TCallback;
begin
c := DoTest(20);
c(1);
end.
Regards,
Ryan Joseph
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Re: [fpc-pascal] C-blocks
Am Do., 15. Nov. 2018, 08:39 hat Ryan Joseph geschrieben: > > > > On Nov 15, 2018, at 1:27 PM, Sven Barth via fpc-pascal < > fpc-pascal@lists.freepascal.org> wrote: > > > > They are only useful when interacting with the external runtime. On > other OSes nothing would support them thus there is no use for them. > Additionally this requires extensive runtime, not to mention Objective C > support. > > There is even less sense in trying to port them as Object Pascal has > anonymous functions which are already Work In Progress for FPC. > > I see, that’s too bad. Anonymous functions appear to be dead as far as I > can tell. In progress since 2012 I think? > Unlike you I'm in active contact with the developer and the last message was only a few months ago. > Would it be permitted to add inline declarations of nested functions as a > temporary replacement? They don’t capture state but at least they solve the > issue of polluting namespace with named functions which you use in only one > location. Better than nothing (since that’s what we’re realistically > looking at) and no new complicated features. > No. This would conflict with the work of Blaise. Also even if we'd add that now it would not make 3.2 as it would be a too invasive change. So the earliest release would be 3.4 and for that I plan to have the real thing integrated into trunk. Thus it would be wasted effort to add that now. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Passing nested procs out?
Am Do., 15. Nov. 2018, 10:17 hat Ryan Joseph geschrieben: > Is passing nested procs outside of the calling scope relying on undefined > behavior? It doesn’t seem like this should be allowed. > See the notes mentioned here: http://wiki.freepascal.org/FPC_New_Features_2.6.0#Support_for_nested_procedure_variables Don't know if it is documented as such, but if not, it should be. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Passing nested procs out?
On Thu, Nov 15, 2018 at 8:15 AM Sven Barth via fpc-pascal wrote: > > Am Do., 15. Nov. 2018, 10:17 hat Ryan Joseph > geschrieben: >> >> Is passing nested procs outside of the calling scope relying on undefined >> behavior? It doesn’t seem like this should be allowed. > > > See the notes mentioned here: > http://wiki.freepascal.org/FPC_New_Features_2.6.0#Support_for_nested_procedure_variables > > Don't know if it is documented as such, but if not, it should be. If I understood correctly, this can be used in all cases of anonymous functions, with the advantage to make the code more readable and "Pascalish". Am I right? regards, Marcos Douglas ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Passing nested procs out?
> On Nov 15, 2018, at 5:14 PM, Sven Barth via fpc-pascal > wrote: > > See the notes mentioned here: > http://wiki.freepascal.org/FPC_New_Features_2.6.0#Support_for_nested_procedure_variables > > Don't know if it is documented as such, but if not, it should be. > Sorry I’m not understanding this. I read we can make the assignment but the part I’m curious about is passing the function pointer out of the nested functions scope. I did some tests and it work in some cases and gave me garbled memory in others. Just wanted to make absolutely certain what’s happening here. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Passing nested procs out?
Am Do., 15. Nov. 2018, 12:26 hat Marcos Douglas B. Santos geschrieben: > On Thu, Nov 15, 2018 at 8:15 AM Sven Barth via fpc-pascal > wrote: > > > > Am Do., 15. Nov. 2018, 10:17 hat Ryan Joseph > geschrieben: > >> > >> Is passing nested procs outside of the calling scope relying on > undefined behavior? It doesn’t seem like this should be allowed. > > > > > > See the notes mentioned here: > http://wiki.freepascal.org/FPC_New_Features_2.6.0#Support_for_nested_procedure_variables > > > > Don't know if it is documented as such, but if not, it should be. > > If I understood correctly, this can be used in all cases of anonymous > functions, with the advantage to make the code more readable and > "Pascalish". > Am I right? > No, because function references (which is the name of the variables for anonymous functions) store the captured variables in an automatically created and managed object. Nested functions simply work on the stack. So passing them outside of the context of the function they're declared in will result in garbage. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Passing nested procs out?
Am Do., 15. Nov. 2018, 12:40 hat Ryan Joseph geschrieben: > > > > On Nov 15, 2018, at 5:14 PM, Sven Barth via fpc-pascal < > fpc-pascal@lists.freepascal.org> wrote: > > > > See the notes mentioned here: > http://wiki.freepascal.org/FPC_New_Features_2.6.0#Support_for_nested_procedure_variables > > > > Don't know if it is documented as such, but if not, it should be. > > > > Sorry I’m not understanding this. I read we can make the assignment but > the part I’m curious about is passing the function pointer out of the > nested functions scope. I did some tests and it work in some cases and gave > me garbled memory in others. Just wanted to make absolutely certain what’s > happening here. > The linked entry answers your question directly: "if you assign a nested routine to nested procedure variable and then exit the nested routine's parent stack frame, calling the nested procedure variable will result in undefined bahaviour [sic]." Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] C-blocks
> On Nov 15, 2018, at 5:09 PM, Sven Barth via fpc-pascal > wrote: > > Unlike you I'm in active contact with the developer and the last message was > only a few months ago. That’s good news then but I’m not going to hold my breath. Best of luck to the man. > > > Would it be permitted to add inline declarations of nested functions as a > temporary replacement? They don’t capture state but at least they solve the > issue of polluting namespace with named functions which you use in only one > location. Better than nothing (since that’s what we’re realistically looking > at) and no new complicated features. > > No. This would conflict with the work of Blaise. Also even if we'd add that > now it would not make 3.2 as it would be a too invasive change. So the > earliest release would be 3.4 and for that I plan to have the real thing > integrated into trunk. Thus it would be wasted effort to add that now. I just went back and read some of old threads of where closure support is at and it was mentioned that closures (i.e. what Delphi is calling anonymous functions) are actually a pretty heavy weight concept and require a non-trivial amount of overheard. Looking at the c-blocks implementation Jonas did the and RTL behind it confirms this to me. Given that, having a light-weight “anonymous nested function” (not a “reference to” closure) is actually a nice compliment and in fact 2 different things. As FPC’s current c-blocks support demonstrates, it has closure properties but NOT anonymous functions (yet), which are indeed 2 distance concepts. Seems to be both are good to have. Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Passing nested procs out?
> On Nov 15, 2018, at 8:24 PM, Sven Barth via fpc-pascal > wrote: > > The linked entry answers your question directly: > > "if you assign a nested routine to nested procedure variable and then exit > the nested routine's parent stack frame, calling the nested procedure > variable will result in undefined bahaviour [sic]." > My fault for not reading more carefully. Sorry Sven! Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] C-blocks
Am Do., 15. Nov. 2018, 15:01 hat Ryan Joseph geschrieben: > Given that, having a light-weight “anonymous nested function” (not a > “reference to” closure) is actually a nice compliment and in fact 2 > different things. As FPC’s current c-blocks support demonstrates, it has > closure properties but NOT anonymous functions (yet), which are indeed 2 > distance concepts. Seems to be both are good to have. > No, too many ways to do the same thing don't make things easier, not to mention that everything needs to be maintained. So this gets a definite "no" from me. Also the overhead for calling an anonymous function is only that for a virtual method call. Regards, Sven > ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] C-blocks
> On Nov 15, 2018, at 11:30 PM, Sven Barth via fpc-pascal > wrote: > > No, too many ways to do the same thing don't make things easier, not to > mention that everything needs to be maintained. So this gets a definite "no" > from me. > > Also the overhead for calling an anonymous function is only that for a > virtual method call. Do you mean if the anonymous function has no state it’s only a single function call? After reading old forum posts it sounded like this was going to be implemented by some reference counted structure which was allocated on the heap and even using interfaces perhaps. Depending on how this is implemented it may not be possible to prevent them from capturing state if the anonymous function accesses variables in the parent scope. How much of that is accurate? Regards, Ryan Joseph ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
