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Showing content from https://github.com/rust-lang/libs-team/issues/268 below:

Implement `into_chars` for `String` · Issue #268 · rust-lang/libs-team · GitHub

Currently there is no owning analog to the chars iterator. In most contexts this has no real effect, as char is Copy, but it disables some cases where one wants to pass ownership of the underlying String along with the iterator.

Implementing the following function requires some gymnastics.

fn get_chars() -> impl Iterator<Item=char> {
    let s = format!("for one reason or another, you have a String");
    s.chars().filter(|c| ['a','e','i','o','u'].contains(c))
    // error[E0597]: `s` does not live long enough
}

If into_chars existed, the above function would be simple to write.

fn get_chars() -> impl Iterator<Item=char> {
    let s = format!("for a very good reason, you have a String");
    s.into_chars().filter(|c| ['a','e','i','o','u'].contains(c))
}

It is relatively straightforward to write an owning chars iterator outside of std. As a struct:

struct IntoChars {
    string: String,
    position: usize,
}

impl Iterator for IntoChars {
    type Item = char;

    fn next(&mut self) -> Option<char> {
        let c = self.string[self.position..].chars().next()?;
        self.position += c.len_utf8();
        Some(c)
    }
}

As a closure:

fn into_chars(s: String) -> impl Iterator<Item = char> {
    let mut i = 0;
    std::iter::from_fn(move ||
        if i < s.len() {
            let c = s[i..].chars().next().unwrap();
            i += c.len_utf8();
            Some(c)
        } else {
            None
        }
    )
}

Discussion on irlo.

kornelski, trentj, RustyYato and thaliaarchi

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