Patrick Walton proposed the idea of a "left-pad index": I went ahead and crunched the numbers for crates.io, surveying the top 500 crates by recent downloads, dividing that number by the crate size, and coming up with the following results: Per Patrick, here are some good candidates for potential inclusion in std: ...the idea being that it would be safer to rely on the Rust distribution itself, rather than individual maintainers of third-party crates, for this functionality.