rust | Empowering everyone to build | Compiler library

This worked as suggeted by nextJS docs but it takes away Rust compiler and all its benefits... Here is what I did for those who eventually get stuck...

Step 1. add this line or edit next.json.js

Is there a way to work around this issue without imposing additional constraints on map key and value types?

It doesn't appear doable in safe Rust, at least not with reasonable algorithmic complexity. (See Aiden4's answer for a solution that does it by re-building the whole map.)

But if you're allowed to use unsafe, and if you're determined enough that you want to delve into it, this code could do it:

You are correct, this is due to match ergonomics. The first case should hopefully be self explanatory, but the second and third cases can be a bit counter-intuitive.

In the second case:

• (x,) is a non-reference pattern (see the second example in the RFC). The t tuple reference is dereferenced, and x is bound as a ref as it also is a non-reference pattern. Note that t.0 was a reference to begin with, thus resulting in x being a double reference.

• (&y,) is also a non-reference pattern. The t tuple is dereferenced again to a (&i32,). However, &y is a reference pattern being matched to a &i32 reference. Hence y is bound with move mode and is an i32.

In the third case:

• Using the same reasoning as the second case, u is dereferenced via Deref coercion to an (i32,), and x, a non-reference pattern, is bound in ref mode. Hence x is an &i32.

• Again with the same reasoning as the second case, u is dereferenced to an (i32,). The &y reference pattern is then matched to an i32, a non-reference, which causes an error.

#[main] is an old, unstable attribute that was mostly removed from the language in 1.53.0. However, the removal missed one line, with the result you see: the attribute had no effect, but it could be used on stable Rust without an error, and conflicted with imported attributes named main. This was a bug, not intended behaviour. It has been fixed as of nightly-2022-02-10 and 1.59.0-beta.8. Your example with use tokio::main; and #[main] can now run without error.

Before it was removed, the unstable #[main] was used to specify the entry point of a program. Alex Crichton described the behaviour of it and related attributes in a 2016 comment on GitHub:

Ah yes, we've got three entry points. I.. think this is how they work:

• First, #[start], the receiver of int argc and char **argv. This is literally the symbol main (or what is called by that symbol generated in the compiler).
• Next, there's #[lang = "start"]. If no #[start] exists in the crate graph then the compiler generates a main function that calls this. This functions receives argc/argv along with a third argument that is a function pointer to the #[main] function (defined below). Importantly, #[lang = "start"] can be located in a library. For example it's located in the standard library (libstd).
• Finally, #[main], the main function for an executable. This is passed no arguments and is called by #[lang = "start"] (if it decides to). The standard library uses this to initialize itself and then call the Rust program. This, if not specified, defaults to fn main at the top.

So to answer your question, this isn't the same as #[start]. To answer your other (possibly not yet asked) question, yes we have too many entry points.

Their relationship is like between cargo build and cargo rustc: cargo doc performs all the usual work, for an entire workspace, including dependencies (by default). cargo rustdoc allows you to pass flags directly to rustdoc, and only works for a single crate.

Here is the execution code for cargo rustdoc. Here is the code for cargo doc. The only differences is that cargo rustdoc always specify to not check dependencies while cargo doc allows you to choose (by default it does, but you can specify the flag --no-deps), and that cargo rustc allows you to pass flags directly to rustdoc with the flags after the --.

Update the Rust to satisfy the new edition 2021.

rustup default nightly && rustup update

Thanks to @ken. Yes, you can use the stable channel too!

But I love nightly personally.

There are many ways to do it. One of the simplest (and arguably most readable) is something like this:

extern "C" on both sides + #[repr(C)] on the Rust side + only using C-compatible types for interfacing between C++ and Rust, should work.

Alternatively, see cxx and autocxx.

Overflow in the iterator state.

The C++ version will loop forever when given a large enough input: