How to define a str const for whole string and their parts?

code review
1

I often have a situation as in the example below:

#![feature(const_index)]
const SCRIPT_EXT: &str = ".7b.sh.mk";

const SHELL_SCRIPT: &str = &SCRIPT_EXT[4..6];

fn main() {
    println!("myscript.{SHELL_SCRIPT}")
}

Unfortunately, this example isn't compilable, because:

error[E0658]: cannot call conditionally-const operator in constants
 --> /media/exhdd/Dev/modu/question/question.rs:4:39
  |
4 | const SHELL_SCRIPT: &str = &SCRIPT_EXT[4..6];
  |                                       ^^^^^^
  |
  = note: calls in constants are limited to constant functions, tuple structs and tuple variants
  = note: see issue #143874 <https://github.com/rust-lang/rust/issues/143874> for more information
  = help: add `#![feature(const_trait_impl)]` to the crate attributes to enable
  = note: this compiler was built on 2026-03-20; consider upgrading it if it is out of date

error: aborting due to 1 previous error

It is arguable why slice isn't constant for a constant range? Okay, I use the solution as below to address it:

fn main() {
    println!("myscript.{}", &SCRIPT_EXT[4..6])
}

But this solution isn't reliable, because if I changed the source string, I will need to change all addressing the string ranges. How do you address the issue? Introduce range (4..6) type or solve it somehow different?

2

You probably want to use static instead of const, since const drops new copies all over the place. And although you can't index in a const context, split_at can be used instead. So something ugly-but-workable could look like:

1 Like
3

Thanks, and static is sufficient only for ranges.