Trait and lifetimes


Given this simple code:

trait AsBytes {
    fn as_bytes(&self) -> &[u8];

fn splitI<'a, I: 'a + AsBytes>(foo: I) -> (I, &'a [u8]) {
    let bytes = foo.as_bytes();
    (foo, bytes)

Rust (1.17) complains that "foo does not live long enough". I thought that, by using I: 'a, I told rust that anything implementing I lives at least as long as 'a, but there is clearly something I’m missing.


I’m not sure about the lifetime annotations, but what you’re trying to do may not be allowed anyway.

In Rust it’s not possible to have a data structure that both owns the data and has a reference to the owned data, such as (foo, &

You can have multiple references though:

fn splitI<'a, I: 'a + AsBytes>(foo: &'a I) -> (&'a I, &'a [u8]) {
    let bytes: &'a _ = foo.as_bytes();
    (foo, bytes)


It’s not allowed, yeah. ‘foo’ is moved in and out of that fn and the reference, if allowed, would point to invalid memory once it’s moved out of the fn.


I see. Thanks for the pointer.