How to initialize generic array with generic-array crate in rust?

Question

struct Foo<N: ArrayLength<i32>> {
    data: GenericArray<i32, N>
}

But it doesn't explain how to initialize value:

impl<N: ArrayLength<i32>> Foo<N> {
    pub fn new() -> Self {
        Self {
            data: // What to puts here?
        }
    }
}

Playground here to help testers.

What do you want to initialize it to? Default values? A specific array? — Frxstrem, Apr 05 '20 at 00:51

score 3 · Accepted Answer · answered Apr 05 '20 at 07:55

You can default-initialize and mutate them afterwards:

let mut data = GenericArray::default();
for x in &mut data {
    *x = 33;
}

Or you can use the GenericArray::from_exact_iter function. The problem is that there does not seem to be an easy way to create an iterator of n elements that also implements ExactSizeIterator. You can implement one though:

struct RepeatN<T>{
    item: T,
    count: usize,
}

impl<T: Clone> Iterator for RepeatN<T> {
    type Item = T;

    fn next(&mut self) -> Option<T> {
        self.count.checked_sub(1).map(|count| {
            self.count = count;
            self.item.clone()
        })
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.count, Some(self.count))
    }
}

impl<T: Clone> ExactSizeIterator for RepeatN<T> {
    fn len(&self) -> usize {
        self.count
    }
}

fn repeat_n<T: Clone>(item: T, count: usize) -> RepeatN<T> {
    RepeatN {
        item,
        count,
    }
}

And use it like GenericArray::from_exact_iter(repeat_n(33, N::to_usize())).unwrap().

How to initialize generic array with generic-array crate in rust?

1 Answers1