Returning a boxed iterator over a value in a structure [duplicate] - iterator

Question

This question already has answers here:
Why is adding a lifetime to a trait with the plus operator (Iterator<Item = &Foo> + 'a) needed?
(1 answer)
What is the correct way to return an Iterator (or any other trait)?
(2 answers)
Closed 5 years ago.
I want a function on a struct which returns an iterator to one of the struct's members. I tried something like the following, which doesn't work.
struct Foo {
bar: Vec<String>,
}
impl Foo {
fn baz(&self) -> Box<Iterator<Item = &String>> {
Box::new(self.bar.iter())
}
}
fn main() {
let x = Foo { bar: vec!["quux".to_string()] };
x.baz();
}
When compiling, I get the error below:
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements
--> src/main.rs:7:27
|
7 | Box::new(self.bar.iter())
| ^^^^
|
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 6:5...
--> src/main.rs:6:5
|
6 | / fn baz(&self) -> Box<Iterator<Item = &String>> {
7 | | Box::new(self.bar.iter())
8 | | }
| |_____^
note: ...so that reference does not outlive borrowed content
--> src/main.rs:7:18
|
7 | Box::new(self.bar.iter())
| ^^^^^^^^
= note: but, the lifetime must be valid for the static lifetime...
note: ...so that expression is assignable (expected std::boxed::Box<std::iter::Iterator<Item=&std::string::String> + 'static>, found std::boxed::Box<std::iter::Iterator<Item=&std::string::String>>)
--> src/main.rs:7:9
|
7 | Box::new(self.bar.iter())
| ^^^^^^^^^^^^^^^^^^^^^^^^^
I also tried adding lifetime information as suggested elsewhere
struct Foo {
bar: Vec<String>,
}
impl Foo {
fn baz<'a>(&self) -> Box<Iterator<Item = &String> + 'a> {
Box::new(self.bar.iter())
}
}
fn main() {
let x = Foo { bar: vec!["quux".to_string()] };
x.baz();
}
Now my error is the following:
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements
--> src/main.rs:7:27
|
7 | Box::new(self.bar.iter())
| ^^^^
|
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 6:5...
--> src/main.rs:6:5
|
6 | / fn baz<'a>(&self) -> Box<Iterator<Item = &String> + 'a> {
7 | | Box::new(self.bar.iter())
8 | | }
| |_____^
note: ...so that reference does not outlive borrowed content
--> src/main.rs:7:18
|
7 | Box::new(self.bar.iter())
| ^^^^^^^^
note: but, the lifetime must be valid for the lifetime 'a as defined on the method body at 6:5...
--> src/main.rs:6:5
|
6 | / fn baz<'a>(&self) -> Box<Iterator<Item = &String> + 'a> {
7 | | Box::new(self.bar.iter())
8 | | }
| |_____^
note: ...so that expression is assignable (expected std::boxed::Box<std::iter::Iterator<Item=&std::string::String> + 'a>, found std::boxed::Box<std::iter::Iterator<Item=&std::string::String>>)
--> src/main.rs:7:9
|
7 | Box::new(self.bar.iter())
| ^^^^^^^^^^^^^^^^^^^^^^^^^