| |||||||||||||
Day: GNOME OSDay: GNOME OSPosted Aug 10, 2012 17:50 UTC (Fri) by slashdot (guest, #22014)In reply to: Day: GNOME OS by slashdot Parent article: Day: GNOME OS
BTW, the REAL idiots here are the guys in the C++ comittee who released a broken unimplementable standard (or alternatively, a standard without a full compatibility goal, which is even worse), despite having had 13 (!!!) years to fix it.
The gcc developers pretty much merely slavishly followed that idiocy without questioning, until they realized their mistake.
(Log in to post comments)
Day: GNOME OS Posted Aug 10, 2012 18:30 UTC (Fri) by nix (subscriber, #2304) [Link]
Er, you do realise that the C++ Standard, following the original STL, has imposed time and space complexity constraints on various parts of the library for a very long time? They're essential, because those constraints are the only difference between some of the Standard's data structures.
This was just a new constraint, which was unfortunately incompatible with the existing implementation of the list<> in GCC, and it was impossible to change it without breaking backward compatibility. (One problem with templated data structures is that a lot of things you wouldn't expect to be ABI concerns actually are, because they are included in programs using them via template expansion.)
Deciding whether to violate the language standard or piss off your users is an unpleasant fork to be in -- but it's not the committee's fault either, because this sort of change is what language standard revisions have always done. C99 broke some valid C89 code: C11 breaks some more. It's just that the set of GCC-compiled code that got broken by a fully conformant implementation of the C++11 list<> was rather large...
Day: GNOME OS Posted Aug 10, 2012 19:13 UTC (Fri) by slashdot (guest, #22014) [Link]
> This was just a new constraint, which was unfortunately incompatible with the existing implementation of the list<> in GCC, and it was impossible to change it without breaking backward compatibility
And that's the problem.
Adding the new constraint by the C++ committee was simply asinine, especially, since you lose O(1) list splicing (and you can keep the size yourself with C++98 std::list, but can't do O(1) splice yourself with C++11 std::list), and because at least one existing implementation could not provide it while keeping compatibility.
They should have added a new type if they wanted C++ to have a linked list with O(1) size().
BTW, they also broke multithreaded programs using std::list, since unless the size field is updated with atomics (which kills performance on several archs), it's no longer true that you can add to the head of a non-empty list in a thread and to the tail in another thread, which would work in C++98 libstdc++.
As for the GCC, I think it should need a separate option to enable ABI-breaking C++11 changes, and --std=c++11 should only enable the backwards compatible C++11 subset, which appears to be what they hint at in the recent announcement.
C++11 is not fully implemented anyway, so that's not an issue for now, and perhaps in the meantime the standard can be revised to revert the changes.
Day: GNOME OS Posted Aug 10, 2012 19:28 UTC (Fri) by juliank (subscriber, #45896) [Link]
If I had to guess, I'd say that the O(1) size() thing was introduced to the standard by Microsoft.
Day: GNOME OS Posted Aug 10, 2012 19:42 UTC (Fri) by juliank (subscriber, #45896) [Link]
OK, it seems to be pushed by Apple via proxy, not Microsoft, as far as I can tell.
|
|||||||||||||