Iterate through Vec<&str> and accumulate value to a variable when condition is fullfilled

Question

My current attempt:

let fruits:Vec<&str> = vec!["Banana", "Peach"];
let fruits_hashmap: HashMap<_, _> = HashMap::from_iter([("Apple", 2),("Banana", 4),("Peach", 8)]);
let mut n = 0;
let c =  fruits.iter().map(|s| 
    
    match fruits_hashmap.get(s) {
        Some(value) => n |= value,
        None => println!("{} does not exist", s)
    });
return n;

But I get warning: unused variable: fruits_hashmap and also n is equal to 0 but it should be equal to 12.

Answer 1

I guess you added let c = because you had another warning before:

warning: unused `Map` that must be used
  --> src/lib.rs:8:5
   |
8  | /     fruits.iter().map(|s| match fruits_hashmap.get(s) {
9  | |         Some(value) => n |= value,
10 | |         None => println!("{} does not exist", s),
11 | |     });
   | |______^
   |
   = note: iterators are lazy and do nothing unless consumed
   = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
   |
8  |     let _ = fruits.iter().map(|s| match fruits_hashmap.get(s) {
   |     +++++++

However, this isn't the solution. As the warning says, iterators are lazy and do nothing unless consumed. What you need is not map(), but a for loop:

for s in &fruits {
    match fruits_hashmap.get(s) {
        Some(value) => n |= value,
        None => println!("{} does not exist", s),
    }
}