将字符串转换为 &str Rust 而不会导致借用问题

Question

Is there someway to convert a String (function parameter) into &str (used in return value) while avoiding borrowing problems or referencing a temporary value.

Here is an example use case:

PS: I am constrained by existing functions to these types and cannot just change the type of the function's parameter nor its &str consuming return value. Also the following example uses clap::Arg::new to emphasize this aspect.

// f is any iterator over String values, for example sake I am using Vec<String> with literal value which does not represent the real case.
let f: Vec<String> = vec!["A".into(),"B".into(),"C".into()].into_iter();

let arg: clap::Arg = f.map(|s: String|{
    clap::Arg::new(s.as_str())
});

Answer 1

Is there someway to convert a String (function parameter) into &str (used in return value) while avoiding borrowing problems or referencing a temporary value.

No but yes, but, really, no.

"No": if your parameter is a String , then the function owns the String , meaning once the function exits the String will be reclaimed, and so any referenced to that would be invalid as it would be dangling.

"but yes": you can convert the String into a Box<str> , which you can thenleak . This returns a &'static str , which will live forever

"but, really, no": while leaking memory is safe as far as Rust is concerned, it's still leaking memory . This might be fine in some contexts (eg short-running processes where explicitly freeing is a waste of resources, or some forms of ad-hoc interning), but in general it's really bad practice.