RS.CLIPPY.LEN_ZERO

Checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead

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

What it does

Checks for getting the length of something via .len() just to compare to zero, and suggests using .is_empty() where applicable.

Why is this bad?

Some structures can answer .is_empty() much faster than calculating their length. So it is good to get into the habit of using .is_empty(), and having it is cheap. Besides, it makes the intent clearer than a manual comparison in some contexts.

Example

if x.len() == 0 {
    ..
}
if y.len() != 0 {
    ..
}

instead use

if x.is_empty() {
    ..
}
if !y.is_empty() {
    ..
}