Qt VS abseil-cpp

Qt mono repo : .. you could check out all submodules and simply use CMake to exactly achieve this. A mono repo also means that if I only use qtbase and declarative, I would need to have all submodules in there? - No

For e.g. if you’re writing a framework, you need to interface with Cocoa on MacOS to draw windows, which only provides an Objective C or Swift interface. You can look at the Qt source code and see how they do it: https://github.com/qt/qtbase/tree/067b53864112c084587fa9a507eb4bde3d50a6e1/src/plugins/platforms/cocoa

That's because Qt 6 wholeheartedly converted to CMake for you. (At least it is better than qmake.) In order to support this Qt has this large battery of CMake files [1]. Qt is of course a clear outlier, but you can't expect the same level of support from every other library you want. My points about "anything exotic" still stand.

[1] https://github.com/qt/qtbase/tree/dev/cmake

What are you talking about? Qt has GTK theme support built-in: https://github.com/qt/qtbase/tree/dev/src/plugins/platformthemes/gtk3

This looks like the Qt bug solved by this commit: https://github.com/qt/qtbase/commit/acaabc9108dfe75530960cf8e3ec4f3602cd82e0

Yeah, I'm sure it's completely unheard of. Oh except that it took me all of a couple minutes to find an example of that exact thing in one of the largest, most commonly used C++ frameworks out there.

I don't see any connect in https://github.com/qt/qtbase/blob/dev/src/corelib/tools/qsharedpointer_impl.h, and QPointer isn't a QObject (though I don't know if the latter is actually necessary for signal-slots). One (unreliable) way to test is to see if a QPointer fails to be nulled out when the QObject is blocked by a QSignalBlocker. Alternatively I'd set a data breakpoint on a QPointer and try it out. But I don't have the time right now.

Yeah, it's nice! And Abseil does it, IFF you use LLVM libc++.

https://github.com/abseil/abseil-cpp/blob/master/absl/string...

The standard adopted it as resize_and_overwrite. Which I think is a little clunky.

This may be confusing to those familiar with Google's libraries. The baseline is the Go BTree, which I personally never heard of until just now, not the C++ absl::btree_set. The benchmarks aren't directly comparable, but the C++ version also comes with good microbenchmark coverage.

https://github.com/google/btree

https://github.com/abseil/abseil-cpp/blob/master/absl/contai...

An implementation of call_once that accommodates callbacks that throw: https://github.com/abseil/abseil-cpp/blob/master/absl/base/c...

I wouldn't say it's that cryptic. It's just a few bitwise rotations/shifts/xor operations.

You can see hashing optimizations as well https://www.deepmind.com/blog/alphadev-discovers-faster-sort..., https://github.com/abseil/abseil-cpp/commit/74eee2aff683cc7d...

I was one of the members who reviewed expertly what has been done both in sorting and hashing. Overall it's more about assembly, finding missed compiler optimizations and balancing between correctness and distribution (in hashing in particular).

It was not revolutionary in a sense it hasn't found completely new approaches but converged to something incomprehensible for humans but relatively good for performance which proves the point that optimal programs are very inhuman.

Note that for instructions in sorting, removing them does not always lead to better performance, for example, instructions can run in parallel and the effect can be less profound. Benchmarks can lie and compiler could do something differently when recompiling the sort3 function which was changed. There was some evidence that the effect can come from the other side.

For hashing it was even funnier, very small strings up to 64 bit already used 3 instructions like add some constant -> multiply 64x64 -> xor upper/lower. For bigger ones the question becomes more complicated, that's why 9-16 was a better spot and it simplified from 2 multiplications to just one and a rotation. Distribution on real workloads was good, it almost passed smhasher and we decided it was good enough to try out in prod. We did not rollback as you can see from abseil :)

But even given all that, it was fascinating to watch how this system was searching and was able to find particular programs can be further simplified. Kudos to everyone involved, it's a great incremental change that can bring more results in the future.

Check out https://abseil.io. It offers absl::optional, which is a backport of std::optional.