[Oberon] Oberon for a C++ user.

[Andreas Pirklbauer]

Felix,
that appears to be a solvable problem though. Two comments:

(i) In order to keep "old" types and methods around, it suffices to keep older versions of a module block (containing both its type descriptors and its procedures) around in main memory, as long as there are references to them from the remaining part of the system.

(ii) Even if an "old" version of a module passes a pointer around and that pointer suddenly ends up in a newer version (of potentially the same module), it is not really a problem (I think, but happy to be proven wrong) - so long as the "old" type descriptors and methods are still available in memory.

Note that "old" methods will of course also access the "old" record and the "old" type descriptor for that record type, so there doesn't seem to be problem in principle. That of course needs to be taken with a grain of salt, just like one needs to take module interfaces with a grain of salt. If the newer version of a module doesn't actually change the module *interface* (i.e. meaning that clients do not need to be recompiled), but significantly changes the semantics of its implementation, there may be issues. All that is really guaranteed is that the module *interface* doesn't change - so even with modules, it is the programmer's responsibility that the *semantics* between multiple versions are "consistent". I'd say it's the same with records and methods.

PS: I have implemented (i), but have not tested an example for (ii) yet. So if someone supplied a short test program for that in this forum, I'd be happy to test and then report on it.

Andreas
-------------------------------------------------------------------------------------------From: Felix Friedrich felix.friedrich at inf.ethz.ch Tue Sep 27 19:11:59 CEST 2016
> But this does not solve other problems coming from the possible > coexistence of an old and new version of a module. If the old module > survives, pointers could be passed around to new modules compromising > the type system.
> I think that any kind of upcall, be it via procedure variables or via > object methods does not go well with module unloading.
> Felix
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.inf.ethz.ch/pipermail/oberon/attachments/20161112/a29b7ced/attachment.html>