Understanding Rust Error E0029

Introduction to Rust Error E0029

Rust Error E0029 occurs when something other than numbers and characters is used for a range in a match expression. The compiler checks that the range is non-empty at compile-time and can only evaluate ranges containing numbers and characters.

Example of Rust Error E0029

#![allow(unused)]
fn main() {
let string = "salutations !";

// The ordering relation for strings cannot be evaluated at compile time,
// so this doesn't work:
match string {
 "hello" ..= "world" => {}
 _ => {}
}
}

In the code above, we attempt to match a string against a range, which results in Rust Error E0029. The ordering relation for strings cannot be evaluated at compile time.

Solution for Rust Error E0029

To solve Rust Error E0029, we can refactor the match expression using a guard instead of a range. This allows us to capture values of an orderable type between two endpoints.

Refactored Code Example

#![allow(unused)]
fn main() {
let string = "salutations !";

// This is a more general version, using a guard:
match string {
 s if s >= "hello" && s <= "world" => {}
 _ => {}
}
}

The refactored code above now utilizes a guard in the match expression, which correctly handles the string comparison at runtime.

Conclusion

In conclusion, Rust Error E0029 occurs when attempting to match non-numeric and non-character values against a range in a match expression. To resolve this error, use a guard in the match expression to capture orderable types between two endpoints.