draft VS rust

I should have said the "latest standard", not "spec", if we're being technical. But EVERY bit of official material is very clear about asserting that C++23 is still a preview/in-progress, not a standard. Saying otherwise is, strictly speaking, incorrect.

https://isocpp.org/std/the-standard

https://www.iso.org/standard/79358.html

https://github.com/cplusplus/draft/blob/main/papers/n4951.md

[3] https://github.com/cplusplus/draft/releases/tag/n4917

*This is a joke, but only barely so.

pdf

I'm currently going through Annex A of C++20, but I can't find the definition of "designator brace-or-equal-initializer", and couldn't find much formal information on it in an obvious way. The newest source on [decl] (https://github.com/cplusplus/draft/blob/main/source/declarations.tex) also doesn't seem to have it. Am I missing anything, or is this a missing definition in the standard grammar?

> I don't have a copy of the standard at hand, can anyone quote the relevant section?

The C++ (draft) standard is on GitHub! [0] Compiling it needs Perl and some LaTeX packages, but is reasonably straightforwards otherwise. In addition, links to specific draft standards can be found on cppreference [1].

But anyways, in the first C++20 post-publication draft (N4868), the wording you're interested in is in multiple sections. Section 22.2.3 Sequence Containers [sequence.reqmts] has Table 78: Optional sequence container operations [tab:container.seq.opt] (starting on page 815), which states that a precondition of pop_back() is that empty() returns false. Section 16.3.2.4 Detailed Specifications [structure.specifications] (page 481) states:

> Preconditions: the conditions that the function assumes to hold whenever it is called; violation of any preconditions results in undefined behavior.

Therefore, calling pop_back() on an empty vector results in undefined behavior.

> Is this something that in practice is implemented in different (exception-throwing) ways?

Based on a quick glance at the major implementations (libc++ 15.0.7 at [2], MSVC at [3], libstdc++ at [4]), it looks like asserts are used. Whether those result in exceptions probably depends on whether the asserts are compiled in in the first place and how they are implemented, but it's definitely not a guaranteed exception.

[0]: https://github.com/cplusplus/draft

[1]: https://en.cppreference.com/w/cpp/links

[2]: https://github.com/llvm/llvm-project/blob/llvmorg-15.0.7/lib...

[3]: https://github.com/llvm/llvm-project/blob/8dfdcc7b7bf66834a7...

[4]: https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=libstdc%2B%2B-v3...

Which standard specifically are you quoting there? I checked an old and a new C++ draft in https://github.com/cplusplus/draft/tree/main/papers, and in neither one did 6.3 have anything like that.

https://github.com/cplusplus/draft/releases/download/n4917/n4917.pdf (page 1, chapter 1 scope):

PRs for C++ are at https://github.com/cplusplus/draft But the discussion for a PR is via https://isocpp.org/std/submit-a-proposal

C/C++

By the way, https://github.com/cplusplus/draft/releases/tag/n4910 , says

Almost fixed the compiler: https://github.com/rust-lang/rust/pull/123325

Rust: A secure, efficient, and modern programming language (omitting ten thousand words). You can simply follow the installation instructions provided on the official website.

Recently did something similar in Rust but for generating SVGs. We've adopted it for snapshot testing of cargo and rustc's output. Don't have a good PR handy for showing Github's rendering of changes in the SVG (text, side-by-side, swiping) but https://github.com/rust-lang/rust/pull/121877/files has newly added SVGs.

To see what is supported, see the screenshot in the docs: https://docs.rs/anstyle-svg/latest/anstyle_svg/

We strongly believe in Rust as a powerful language for building production-grade software, especially for systems like ours that run alongside Kubernetes.

The above Assert<{N % 2 == 1}> requires #![feature(generic_const_exprs)] and the nightly toolchain. See https://github.com/rust-lang/rust/issues/76560 for more info.

Another week, another dive into Rust. This time, we're delving into structs. Structs bear resemblance to interfaces in TypeScript, enabling the grouping of intricate data sets within an object, much like TypeScript/JavaScript. Rust also accommodates functions within these structs, offering a semblance of classes, albeit with distinctions. Let's delve into this topic.

There’s also other reasons. For example, take binary search:

* prefetch + cmov. These should be part of the STL but languages and compilers struggle to emit the cmov properly (Rust’s been broken for 6 years: https://github.com/rust-lang/rust/issues/53823). Prefetch is an interesting one because while you do optimize the binary search in a micro benchmark, you’re potentially putting extra pressure on the cache with “garbage” data which means it’s a greedy optimization that might hurt surrounding code. Probably should have separate implementations as binary search isn’t necessarily always in the hot path.

* Eytzinger layout has additional limitations that are often not discussed when pointing out “hey this is faster”. Adding elements is non-trivial since you first have to add + sort (as you would for binary search) and then rebuild a new parallel eytzinger layout from scratch (i.e. you’d have it be an index of pointers rather than the values themselves which adds memory overhead + indirection for the comparisons). You can’t find the “insertion” position for non-existent elements which means it can’t be used for std::lower_bound (i.e. if the element doesn’t exist, you just get None back instead of Err(position where it can be slotted in to maintain order).

Basically, optimizations can sometimes rely on changing the problem domain so that you can trade off features of the algorithm against the runtime. These kinds of algorithms can be a bad fit for a standard library which aims to be a toolbox of “good enough” algorithms and data structures for problems that appear very very frequently. Or they could be part of the standard library toolkit just under a different name but you also have to balance that against maintenance concerns.