Rust has builtin types &'static str for strings that live for the entire runtime of the program and ~str for strings that live in dynamically managed heap memor

Rust has builtin types &'static str for strings that live for the entire runtime of the program and ~str for strings that live in dynamically managed heap memory (from the more general ~T for T that live there with T=str). If the function always returns a static string it can return the former type and won't need a ~ or any allocations for that. If you need something more dynamic... you could have a user-defined type that can hold either and remembers whether it's responsible for freeing the memory, but that doesn't fall out of the builtin types naturally.