Comment by burntsushi

> or you yolo it with reserve+set_len, which is invalid Rust because you didn't properly use MaybeUninit for locations which are only ever written

`Vec::spare_capacity_mut`[1] gives you a view into the unused capacity. There's nothing "invalid" about it.

[1]: https://doc.rust-lang.org/std/vec/struct.Vec.html#method.spa...