CODEWITHSUNDEEP
rust
John Difool
John Difool

Reputation: 5702

Deconstructing struct wrapped in a Mutex

I wrote this example (not working):

use std::sync::Mutex;
use std::ops::Deref;

pub struct DBAndCFs {
    db: i32,
    cfs: Vec<i32>,
}

fn main() {
    let x: Mutex<Option<DBAndCFs>> = Mutex::new(Some(DBAndCFs{ db: 0, cfs: Vec::new() } ));
    let DBAndCFs { ref db, ref cfs } = x.lock().unwrap().deref();
}

I have been following the docs but I am still unable to assign the dband cfsfields to the variables on the left.

Upvotes: 1

Views: 751

Answers (1)

Chayim Friedman
Chayim Friedman

Reputation: 70860

Mutex::lock() returns Result<MutexGuard, PoisonError>. The first .unwrap() unwraps this Result. You need another .unwrap() to unwrap the Option, and also .as_ref() to not move out of it:

let DBAndCFs { ref db, ref cfs } = x.lock().unwrap().as_ref().unwrap();

You also don't need the ref because of match ergonomics (see What does pattern-matching a non-reference against a reference do in Rust?):

let DBAndCFs { db, cfs } = x.lock().unwrap().as_ref().unwrap();

Upvotes: 4

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