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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Error with function return value

The following code does not compile and gives the error: error[E0515]: cannot return value referencing local variable 'map'

use std::collections::HashMap;

#[derive(Debug)]
struct Ctx<'a> {
    map: HashMap<u32, String>,
    vec: Vec<&'a str>,
}

fn mk_ctx<'a>() -> Ctx<'a> {
    let map: HashMap<u32, String> = HashMap::from([(0, "foo".into())]);
    let vec: Vec<&str> = mk_vec(&map);

    Ctx { map, vec }
}

fn mk_vec(map: &HashMap<u32, String>) -> Vec<&str> {
    todo!()
}

fn main() {
    let res = mk_ctx();
    println!("{res:?}")
}

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As far as I understand due to map being a parameter to mk_vec and by applying lifetime elision rules, the &str in vec will have the same lifetime as map. At the end of mk_ctx map is moved to ctx.map. I would assume that vec can be moved to ctx.vec as well.

What is the issue here and how can the code be fixed?

10 posts - 5 participants

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