What can C++ do that Rust can’t? (2021 edition)

https://www.reddit.com/r/rust/comments/n7rjfk/what_can_c_do_that_rust_cant_2021_edition/?utm_source=share&utm_medium=ios_app&utm_name=iossmf

What can C++ do that Rust can’t? (2021 edition)

What can C++ do that Rust can’t? (2021 edition)

*(Mostly based on [this post](https://www.reddit.com/r/rust/comments/5ti9fc/what_can_c_do_that_rust_cant/).)*

***More suggestions and especially answers/corrections are welcome. I plan to read the comments and update the list.***

**Legend:**

* **Question**
* ~~Will be solved in the near future~~
* *A feature of debatable usefullness*

**Main:**

* **How advanced is Rust’s `const` compared to `constexpr`? How much of the Standard Library is covered by it? I very much support the modern C++ philosophy of “`constexpr` everything (or as much as the compiler can)”, so I’m interested in how Rust is approaching this.**
* ~~Const generics in Stable~~
* ~~Non-integral const generics~~
* **After we get const generics, will C++ templates have any practical advantages over Rust’s generics, apart from variadics? For example, will it be possible to write a Rust version of [`bounded::integer`](https://github.com/davidstone/bounded-integer)?**
* *Variadic templates + overloading by arity (no need for [some?] macros?)*
* **Does the C++ Stndard Library have anything of use that the Rust one doesn’t?**
* *Function overloading (controversial, but there’s a good [argument](https://www.reddit.com/r/rust/comments/5ti9fc/what_can_c_do_that_rust_cant/dk5li7f/) in favour of it, at least if it’s kept limited enough)*
* **Can you implement a trait for a whole class of types? For example, all integral types? C++ lets you do that with SFINAE, and C++20 makes it easier and prettier with concepts.**
* [Delegation of implementation](https://github.com/rust-lang/rfcs/pull/1406/) (done in C++ with nasty inheritance, but still)
* **Is `index` still as limited as [this comment](https://www.reddit.com/r/rust/comments/5ti9fc/what_can_c_do_that_rust_cant/ddmzqng/) says? And how much of a problem is it? I don’t have enough experience with Rust to tell myself.**
* *Automatic initialization of objects by field order*
* *Internal vtables (an optimization for a common case; if you know the set of functions up-front, you can deal with that more efficiently)*
* **How small can Rust executables get with dynamic linking compared to equivalent C++ executables? Does Rust have a stdlib package that you can simply add as a dependency to your dynamically linked programs (just as C++ binaries depend on its own Standard Library shared objects being present in the system), or does it require some black magic? Will non-stable ABI create problems?**
* `decltype`
* Memory model
* Language specification
* More existing library support
* **Note to self: look over modern C++ features, see if there’s anything useful Rust hasn’t had for ages.**