CODEWITHSUNDEEP
rust
g14u
g14u

Reputation: 247

Panic when unwrapping HashMap with None value

fn pair_finder(pairs_length: u64) {
    let mut path: HashMap<u64, u64> = HashMap::new();

        for i in 0..pairs_length {
            if (metadata.token0 == pair_metadata.token0)
                || (metadata.token0 == pair_metadata.token1)
                || (i == *path.get(&current_depth).unwrap())
            {
                continue;
            }
    }
}

I have a function which includes the above block. Path is a HashMap where first u64 is ID of path and second u64 is pair ID. current_depth used is the part of loop where it increases after something new to path is added.

However it panicked. It is because I used the i == *path.get(&current_depth).unwrap() in the if block. And HashMapis empty at current_depth and it got a None value. Are there any way to prevent panic on None and consider that block of if as false?

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/main.rs:69:52

Upvotes: 2

Views: 516

Answers (1)

Leo
Leo

Reputation: 229

Option<T> implements Eq whenever T implements Eq. This means that you can directly compare variants of the Option type, like this:

assert!(Some(1) == Some(1));
assert!(None::<i32> == None);
assert!(Some(1) != Some(2));
assert!(Some(1) != None);

So instead of writing this, which panics if maybe_v is the None variant:

maybe_v.unwrap() == a

You could write this, which just evaluates to false if maybe_v is the None variant:

maybe_v == Some(a)

So in your case, you can write:

fn pair_finder(pairs_length: u64) {
    let mut path: HashMap<u64, u64> = HashMap::new();

        for i in 0..pairs_length {
            if (metadata.token0 == pair_metadata.token0)
                || (metadata.token0 == pair_metadata.token1)
                || (Some(&i) == path.get(&current_depth))
            {
                continue;
            }
    }
}

Upvotes: 7

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