Rust newbie question My understanding is that almost always

Question

Rust newbie question My understanding is that almost always you want to use ` amp str` instead of `String` for a function s argument as it s more flexible Same with using slices in args In a couple of our workunit functions like `with workunit` we use `String` Do you know if that s for a particular reason

hundreds-father-404 · Answer

gt Same with using slices in args Iiuc ` amp str` is a type of slice

enough-analyst-54434 · Answer

If you see an amp there is a lifetime involved If you have a future you need the static lifetime which you can t get for a dynamic string value so you tend to need ownership String gives you that

witty-crayon-22786 · Answer

there can be good reasons to take an owned value as well

witty-crayon-22786 · Answer

in the workunit case the ownership of the given String moves into the workunit ie it lives on beyond the end of the function

witty-crayon-22786 · Answer

if that function boundary were to take a ` amp str` the caller might create a `String` and throw it away and the callee would need to copy it

witty-crayon-22786 · Answer

there are ways to maybe clone things the `Cow` type but you only need them if the callee is not definitely going to take ownership

witty-crayon-22786 · Answer

and one more bit of spiel the ` amp str` `String` borrowed owned dichotomy extends to a bunch of other types including ` amp T ` `Vec lt T gt ` `Path` `PathBuf` etc

enough-analyst-54434 · Answer

This is the poster child for the ownership section in the book Presumably you re reading that but in case you missed it <https doc rust lang org book ch04 01 what is ownership html>