I think all the current uses of once_cell in gitoxide could be replaced by https://doc.rust-lang.org/std/cell/struct.LazyCell.html (stable since Rust 1.80), or by https://doc.rust-lang.org/std/cell/struct.OnceCell.html , or by https://doc.rust-lang.org/std/sync/struct.LazyLock.html if thread-safety is needed.