RS.CLIPPY.REVERSED_EMPTY_RANGES

Reversing the limits of range expressions, resulting in empty ranges

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: reversed_empty_ranges. Copyright ©2025 The Rust Team. All rights reserved.

What it does

Checks for range expressions x..y where both x and y are constant and x is greater to y. Also triggers if x is equal to y when they are conditions to a for loop.

Why is this bad?

Empty ranges yield no values so iterating them is a no-op. Moreover, trying to use a reversed range to index a slice will panic at run-time.

Example

fn main() {
    (10..=0).for_each(|x| println!("{}", x));

    let arr = [1, 2, 3, 4, 5];
    let sub = &arr[3..1];
}

Use instead:

fn main() {
    (0..=10).rev().for_each(|x| println!("{}", x));

    let arr = [1, 2, 3, 4, 5];
    let sub = &arr[1..3];
}

Past names

reverse_range_loop