gen keyword

Summary

• gen is a reserved keyword.

Details

The gen keyword has been reserved as part of RFC #3513 to introduce "gen blocks" in a future release of Rust. gen blocks will provide a way to make it easier to write certain kinds of iterators. Reserving the keyword now will make it easier to stabilize gen blocks before the next edition.

Migration

Introducing the gen keyword can cause a problem for any identifiers that are already called gen. For example, any variable or function name called gen would clash with the new keyword. To overcome this, Rust supports the r# prefix for a raw identifier, which allows identifiers to overlap with keywords.

The keyword_idents_2024 lint will automatically modify any identifier named gen to be r#gen so that code continues to work on both editions. This lint is part of the rust-2024-compatibility lint group, which will automatically be applied when running cargo fix --edition. To migrate your code to be Rust 2024 Edition compatible, run:

cargo fix --edition

For example, this will change:

fn gen() {
    println!("generating!");
}

fn main() {
    gen();
}

to be:

fn r#gen() {
    println!("generating!");
}

fn main() {
    r#gen();
}

Alternatively, you can manually enable the lint to find places where gen identifiers need to be modified to r#gen:

#![allow(unused)]
fn main() {
// Add this to the root of your crate to do a manual migration.
#![warn(keyword_idents_2024)]
}