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

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

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

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

Am Do., 15. Nov. 2018, 12:26 hat Marcos Douglas B. Santos geschrieben:

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

Am Do., 15. Nov. 2018, 12:40 hat Ryan Joseph
geschrieben:

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

My fault for not reading more carefully. Sorry Sven!

Regards,
Ryan Joseph