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impl Trait causes "borrowed value does not live long enough" #50823

cuviper opened this Issue May 17, 2018 · 1 comment


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cuviper commented May 17, 2018

This code:

fn main() {
    println!("{:?}", max());

fn max() -> Option<i32> {
    let v = vec![1, 2, 3];

fn iter(a: &[i32]) -> impl Iterator<Item = i32> + '_ {

gives this error:

error[E0597]: `v` does not live long enough
 --> src/
7 |     iter(&v).max()
  |           ^ borrowed value does not live long enough
8 | }
  | - `v` dropped here while still borrowed
  = note: values in a scope are dropped in the opposite order they are created

But if I change the return type to an explicit std::iter::Cloned<std::slice::Iter<'_, i32>>, then it's fine. It's also fine if I bind that result before returning it, like: let m = iter(&v).max(); m

And it works with #![feature(nll)], so maybe I just have to hope for that to stabilize soon... 🙏


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pnkfelix commented Sep 13, 2018

BTW NLL is turned on as part of the 2018 edition, so if you upgrade to that, this example will start working:

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