[dikaiosune]

Is there an equivalent guide to the compile-time representation of important constructs for those trying to learn C/C++? I haven't seen anything like that and it seems like most devs in that realm instead rely on experience and tribal knowledge (which is, AFAICT, how it often works in Rust-land right now). I agree it'd be great for Rust to have clearer official docs about some of these things, but it doesn't seem to me like this is readily available for most languages or runtimes.

Re: unsafe, I think that's tough. My personal feeling is that many of Rust's selling points rely on minimizing the use of unsafe (i.e. limiting segfault-relevant portions of the code), and that there are frequently ways to make things work and also make them fast without using unsafe. What's an example where you found yourself thinking about using unsafe instead of a more complex safe construct?

(Somewhat related to this, and especially for anyone reading who might try Rust, I cannot recommend getting on IRC strongly enough. The Rust IRC channels are by and large incredibly friendly and helpful, and for better or worse that's where a lot of the knowledge in the community is currently collected, not as much SO or blogs)

[cheepin]

> Is there an equivalent guide to the compile-time representation of important constructs for those trying to learn C/C++?

Definitely. It was taught in school and there's pretty good guides for it online (maybe not caught up to c++11 and beyond, but the fundamentals are there). You're right that it is not readily available for most languages, but when you need to get serious about performance you either are going to have a guide or spend a lot of time looking at assembly/bytecode. To be fair, I'd probably still have to inspect generated code sometimes, but it's nice to have good instincts for how things run to guide your design/implementation so you can spend less time looking at assembly.

http://www.agner.org/optimize/optimizing_cpp.pdf

[dikaiosune]

I definitely haven't seen anything as comprehensive as the linked PDF for Rust (although that shouldn't be surprising given the extreme thoroughness of that guide and the age of C++). Probably a good project!

When doing very performance sensitive things in Rust, I usually find myself asking questions a lot on IRC and looking at disassembly in perf.

To answer some specific examples you cited above: I'm pretty sure that enums are (almost?) always equivalent to tagged unions. If you have an enum which doesn't contain any data, then I believe it's representation is just the tag. Iterators are just structs with methods, the various generic functions they implement are monomorphized and then optimized by LLVM.