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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Struggling with multiple mutable borrows

Can you please teach me what would be the correct, "Rust way" to achieve what I am trying to do?

My expectation is that:

• I call a.find_foo_identifier
• find_foo_identifier returns &str, and I expect this reference to be directly copied from the foo array, from the borrowed value from inside the Vec, which I got from iter() - in fact, I have this map call in which I do the dereference all the way down to &str.
• And because of this copy, I expect that this should release a from being borrowed, because the data is copied from it.
• And then I call push_foo., mutate a, all clean
• And then I call push_bar , mutate a again, all good clean

What instead happens:

• push_foo requires mutable borrow
• push_bar requires mutable borrow
• compiler doesn't allow me to have them at the same time
• and find_foo_identifier does an immutable borrow, and it's not compatible with either of the mutable borrows.

It's as if everything is just in a permanent borrowed state, shouldn't it be, like, released after the reference is done being used?

I am observing an error at a.push_foo("very good");. It says: "cannot borrow a as mutable because it is also borrowed as immutable"

Question: how can I achieve what I'm trying to do in the proper Rust way, so that the borrow checker is satisfied?

Code in question:

struct A<'a> {
    foo: Vec<&'a str>,
    bar: Vec<&'a str>,
}

impl<'a> A<'a> {
    pub fn find_foo_identifier(&self, identifier: &str) -> Option<&str> {
        self.foo.iter()
            .find(|local_node| **local_node == identifier)
            .map(|s|*s)
    }
    fn push_foo(&mut self, s: &'a str) {
        self.foo.push(s);
    }
    fn push_bar(&mut self, s: &'a str) {
        self.bar.push(s);
    }
}

fn build_a<'a>() -> A<'a> {
    let mut a = A { foo: vec![], bar: vec![] };

    for _ in 0..20 {
        let found = a.find_foo_identifier("asdf");

        if let Some(s) = found {
            a.push_foo("very good");
            a.push_bar(s);
        }
    }

    a
}

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