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Description
In this reddit thread a user commented on their confusion with an error message.
The problem is that the lifetime error for this code mentions Iterator twice in the error message instead the types whose lifetimes don't match.
The code that triggers the bug:
use std::marker::PhantomData;
struct AnIterator<'a> {
first: String,
_marker:PhantomData<&'a str>
}
impl<'a> Iterator for AnIterator<'a> {
type Item = &'a str;
fn next<'b>(&'b mut self) -> Option<Self::Item> {
Some(self.first.as_str())
}
}
The error message:
Compiling playground v0.0.1 (/playground)
error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
--> src/lib.rs:12:25
|
12 | Some(self.first.as_str())
| ^^^^^^
|
note: first, the lifetime cannot outlive the lifetime 'b as defined on the method body at 11:13...
--> src/lib.rs:11:13
|
11 | fn next<'b>(&'b mut self) -> Option<Self::Item> {
| ^^
note: ...so that reference does not outlive borrowed content
--> src/lib.rs:12:14
|
12 | Some(self.first.as_str())
| ^^^^^^^^^^
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 8:6...
--> src/lib.rs:8:6
|
8 | impl<'a> Iterator for AnIterator<'a> {
| ^^
= note: ...so that the types are compatible:
expected std::iter::Iterator
found std::iter::Iterator
error: aborting due to previous error
For more information about this error, try `rustc --explain E0495`.
error: Could not compile `playground`.
Here in the last note,instead of saying expected std::iter::Iterator found std::iter::Iterator,
it should be expected &'a str found &'b str.
It prints the correct error message if I change ->Option<Self::Item> to ->Option<&'a str>.