how to do indirection

[PascalDragon]

Yes, it would probably be best to forbid that mode in units...

[Thaddy]

But note ISO standard 10206 (a.k.a. extended pascal) supports modules and I believe FPC has already some features from extended pascal?

[PascalDragon]

But that is a different mode. 

[Thaddy]

Ok. You are able to block it for units, so plz do! 
My point was just that if modules get supported in ExtPas mode a similar concept like units is in place.

(And extpas is an ISO mode, although maybe much like $delphi and $delphiunicode, Oh well, no: the ISO modes are downwards compatible)

[ahydra]

What Jamie and furious wrote is the normal way of doing this for non-OO routines. For OO, you can do some pretty powerful things with TMethod and CodePointer types. CodePointer is an "untyped function pointer" and TMethod can construct a class instance method call out of a CodePointer and a class instance. Then you typecast the TMethod to a function pointer of the appropriate signature and call it, like this:

Code: Pascal  [Select][+][-]

1. type
2.   TFunc = function(const x: int64): int64;
3.  
4. var
5.   c: CodePointer;
6.   m: TMethod;
7.   value: int64;
8.  
9. if condition then c := @TMyClass.FooImplementation else c := @TMyClass.BarImplementation; // these can be instance methods or class methods. they have signature matching TFunc
10.  
11. ...
12.  
13. m.Code = c;
14. m.Data = instance_of_tmyclass;
15. value := TFunc(m)(12345);
16.