Iterate over inner field in struct - rust

Question

I want to implement a Iterator for a struct so easily loop over an inner field but I can't get it to work.
The return from IterWrapper::next() is faulty.
Maybe there is an easier solution to accomplish this.
struct Wrapper {
pub items: Vec<String>
}
struct IterWrapper<'a> {
inner: &'a std::slice::Iter<'a, String>,
}
impl<'a> Iterator for IterWrapper<'a> {
type Item = &'a String;
fn next(&mut self) -> Option<Self::Item> {
self.inner.next();
}
}
impl Wrapper {
fn iter<'a>(&'a self) -> IterWrapper<'a> {
IterWrapper {
inner: &self.items.iter(),
}
}
}
fn main() {
let w = Wrapper {
items: vec![String::from("test1"), String::from("test2")]
};
for item in w.iter() {
println!("{}", item);
}
}
error[E0308]: mismatched types
--> src/main.rs:13:27
|
13 | fn next(&mut self) -> Option<Self::Item> {
| ---- ^^^^^^^^^^^^^^^^^^ expected enum `std::option::Option`, found `()`
| |
| implicitly returns `()` as its body has no tail or `return` expression
14 | self.inner.next();
| - help: consider removing this semicolon
|
= note: expected enum `std::option::Option<&std::string::String>`
found unit type `()`

Answer 1

There are a couple changes that you have to make:
struct Wrapper {
pub items: Vec<String>
}
struct IterWrapper<'a> {
// this needs to own the iterator, not a reference to it
// in order to avoid returning a borrowed value
inner: std::slice::Iter<'a, String>,
}
impl<'a> Iterator for IterWrapper<'a> {
type Item = &'a String;
fn next(&mut self) -> Option<Self::Item> {
// no semicolon here so the result is implicitly returned
// your old error happened because the semicolon causes the value to not be returned
self.inner.next()
}
}
impl Wrapper {
fn iter<'a>(&'a self) -> IterWrapper<'a> {
IterWrapper {
// give the iterator, not the reference to it
inner: self.items.iter(),
}
}
}
fn main() {
let w = Wrapper {
items: vec![String::from("test1"), String::from("test2")]
};
for item in w.iter() {
println!("{}", item);
}
}