abseil-cpp VS GSL

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.

Already showed you how to use ranges and such above, gsl::final_action is here

For span I would recommend the guideline support library - gsl::span

Not sure how things are at this point so you might want to look up with those keywords, but a few years back clang-tidy was one of the suggested tools, or enabling the core guidelines checker in visual studio if you're using that. Maybe using GSL or something similar as well.

When I want safety guarantees, I use the original and run-time checked gsl::span, rather than std::span. https://github.com/microsoft/GSL .

Another solution: use std::span (or some alternative implementations if the codebase doesn't use C++20).

If you ask me, the GSL [1] alone is a fairly radical departure from C++ that delivers a lot of safety. I don't know if it's gotten much popularity, though. Probably because it introduces a similar disruption like you might find from a brand new programming language.

[1] https://github.com/microsoft/GSL

> With Rust, though, one needs to learn entirely new ideas — things like lifetimes, ownership, and the borrow checker. These are not familiar concepts to most people working in other common languages ... Some of those “new” ideas are, of course, present in other languages — especially functional ones.

With C++, lifetime and ownership are just about as important but unfortunately no one's got your back. You can ignore lifetimes and ownership but you do so at your own peril. And the compiler won't tell you you're doing it wrong because the language wasn't designed for it to do so.

If you want a taste of rust's "mindset" (with respect to limitations imposed by some types) without jumping ship to a new language, try C++'s Guidelines Support Library [1]. It introduces some of the same benefits/friction as switching to rust but without a new language. Opting-in to some of these guidelines might be a gentler way to get some of the benefits of Rust. But it comes with a similarly higher bar.

[1] https://github.com/microsoft/GSL

It's also far more verbose than T* or T& (probably intentionally). If you really want a non-nullable pointer, gsl::not_null from the GSL is a good option. Writing your own version is also trivial, if you don't want to add a dependency.

I instead use the GSL and the Core Guidelines, where