[Proposal] bindable expression in if let must be available to borrow in else branch

[KalitaAlexey]

Let's assume code

let mut map = HashMap::new();
for item in &items {
    if let Some(values) = map.get_mut(&item) {
        values.push(0);
    } else {
        // This is error now
        map.insert(item, vec![0]);
    }
}

map is borrowed in if let and being borrowed even if binding failed

[apasel422]

While what you are proposing is potentially useful for other reasons, your specific example can be rewritten to use the entry API (which is additionally more efficient because it only performs one key lookup):

use std::collections::HashMap;

fn main() {
    let items = vec!['a', 'b', 'c', 'a', 'b', 'b'];

    let mut map = HashMap::new();

    for item in &items {
        map.entry(item).or_insert(vec![]).push(0);
    }

    println!("{:?}", map);
}

Prints:

{'c': [0], 'b': [0, 0, 0], 'a': [0, 0]}

[oli-obk]

duplicate of #811

[steveklabnik]

Yes, @oli-obk is correct.