Returning a borrowing iterator in Rust

An iterator over borrowed data ties its lifetime to the collection.

struct Tour {
    steps: Vec<String>,
}

impl Tour {
    fn titles(&self) -> impl Iterator<Item = &str> + '_ {
        self.steps.iter().map(|s| s.as_str())
    }

    fn scripts(&self) -> impl Iterator<Item = &String> + '_ {
        self.steps.iter().filter(|s| s.ends_with(".rs"))
    }
}

fn main() {
    let tour = Tour {
        steps: vec!["Slices".to_string(), "shapes.rs".to_string()],
    };
    println!("{:?}", tour.titles().collect::<Vec<&str>>());
    println!("{}", tour.scripts().count());
}

How it works

1. The returned iterator borrows self, so self must outlive it.
2. impl Iterator<Item = &str> + '_ names that borrow.
3. No allocation happens: the items are slices into the original.

Keywords and builtins used here

• Iterator
• String
• Tour
• Vec
• _
• fn
• impl
• let
• main
• scripts
• self
• str
• struct
• titles
• vec

The run, in numbers

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21

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Type this snippet

Step 2 of 2 in Borrowing without copying, step 6 of 11 in Lifetimes & interior mutability.

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