borrow.rs

// extended from example at:
// https://willmurphyscode.net/2018/04/25/fixing-a-simple-lifetime-error-in-rust/

pub struct SomeCollection<'a> {
    strings: Vec<&'a str>,
}

impl<'a> SomeCollection<'a> {
    pub fn new() -> Self {
        SomeCollection {
            strings: Vec::new(),
        }
    }

    pub fn insert(&mut self, s: &'a str) {
        self.strings.push(s);
    }

    // an attempt to avoid the borrow error, see below
    pub fn insert_push(&mut self, v: &'a mut Vec<String>, value: String) {
        // store in vector
        v.push(value);

        // get reference to just-stored item
        let vp = v.last().unwrap();

        // store reference in collection
        self.insert(vp);
    }

    // another attempt at avoiding the borrow error, see below
    pub fn insert_last(&mut self, v: &'a Vec<String>) {
        self.strings.push(v.last().unwrap());
    }
}

#[cfg(test)]
mod tests {
    use super::SomeCollection;

    #[test]
    fn test() {
        let mut storage = Vec::new();
        let mut my_collection = SomeCollection::new();

        (0..10).for_each(|item| {
            let value = format!("value number {}", item + 1);

            // error: borrow of moved value (rust doesn't update the reference, sure, understandable)
            //storage.push(value);
            //my_collection.insert(&value);

            // error: borrowed data escapes outside of closure
            storage.push(value);
            my_collection.insert(storage.last().unwrap());

            // error: borrowed data escapes outside of closure
            //storage.push(value);
            //my_collection.insert_last(&storage);

            // error: borrowed data escapes outside of closure
            //my_collection.insert_push(&mut storage, value);
        });
    }
}