CODEWITHSUNDEEP
iteratorrust
James Hinshelwood
James Hinshelwood

Reputation: 23

How do I return an iterator over a 2D array with the enumeration indices included?

I have a struct containing a 2D array:

struct Block;

struct World {
    blocks: [[Block; 10]; 10],
}

How could I write a function which returns an iterator over a 2D array, but with the enumeration indices included?

fn enumerate_blocks(&self) -> impl Iterator<Item = (usize, usize, &Block)>

I managed to write an implementation of the function which just returns an iterator without enumeration indices:

fn blocks(&self) -> impl Iterator<Item = &Block> {
    self.blocks.iter().flat_map(|x| x.iter())
}

If I call Iterator::enumerate once, I will get an iterator over (usize, [B; 10])s. What I can do next to get an iterator over (usize, usize, B)s?

I know I could make the function return a custom struct then implement Iterator, like image does, but ideally I would like to avoid this.

Upvotes: 2

Views: 1671

Answers (1)

Shepmaster
Shepmaster

Reputation: 430961

If I call Iterator::enumerate once, I will get an iterator over (usize, [B; 10])s. What I can do next to get an iterator over (usize, usize, B)s?

Call Iterator::enumerate on the inner array in the same way, continuing to use Iterator::flat_map to combine them. Use Iterator::map to add the outer index to the inner tuple.

#[derive(Debug, Default)]
struct Block;

#[derive(Debug, Default)]
struct World {
    blocks: [[Block; 2]; 3],
}

impl World {
    fn blocks(&self) -> impl Iterator<Item = (usize, usize, &Block)> {
        self.blocks
            .iter()
            .enumerate()
            .flat_map(|(x, v)| v.iter().enumerate().map(move |(y, v)| (x, y, v)))
    }
}

fn main() {
    let w = World::default();
    for (x, y, v) in w.blocks() {
        println!("{}, {}, {:?}", x, y, v)
    }
}

0, 0, Block
0, 1, Block
1, 0, Block
1, 1, Block
2, 0, Block
2, 1, Block

Upvotes: 3

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