Iterator on slice references lifetime issue [duplicate] - rust

Question

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Iterator lifetime issue when returning references to inner collection
(2 answers)
Why is adding a lifetime to a trait with the plus operator (Iterator<Item = &Foo> + 'a) needed?
(1 answer)
Closed 7 months ago.
I'm trying to mapped index into a slice given a transformation function, returning an iterator, here the example code:
pub trait MappedIdxIter<T> {
fn map_idx(&self, transform_func: fn(idx: usize, max: usize) -> Option<usize>,) -> Box<dyn Iterator<Item = T>>;
}
impl<'a, U: 'a> MappedIdxIter<&'a U> for [U] {
fn map_idx(&self, transform_func: fn(idx: usize, max: usize) -> Option<usize>,) -> Box<dyn Iterator<Item = &'a U>> {
let max = self.len();
let iter = (0..max).into_iter()
.filter_map(|i| transform_func(i, max))
.map(|i| &self[i]);
Box::new(iter)
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn should_return_even_idx_values() {
let list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
let mapped: Vec<&u32> = list.map_idx(|i, m|
if (i * 2) < m { Some(i * 2) } else { None }
).collect();
assert_eq!([&0, &2, &4, &6, &8], mapped[..]);
}
#[test]
fn should_return_1_5_3() {
let list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
let mapped: Vec<&u32> = list
.map_idx(|i, _m| match i {
0 => Some(1),
1 => Some(5),
2 => Some(3),
_ => None,
})
.collect();
assert_eq!([&1, &5, &3], mapped[..]);
}
}
Rust playground
I'm getting the following error
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements
--> src/priority_list.rs:107:27
|
107 | .map(|i| &self[i]);
| ^^^^^^^
|
How can tell rust that the iterator is only valid for the lifetime of self?
There is some pointers here https://users.rust-lang.org/t/how-to-write-trait-which-returns-an-iterator/44828 but I failed to make it work.
EDIT:
I've been able to implement this using awesome nougat crate, see comment