How to return slice of a vector in a struct

August 15, 2023

I want to return a slice of my vector, but the compiler is complaining that &[Letter] needs an explicit lifetime.

struct Board {
    board: Vec<Letter>,
    width: usize,
    height: usize,
}

impl std::ops::Index<usize> for Board {
    type Output = &[Letter];

    fn index(&self, index: usize) -> &Self::Output {
        return &&self.board[index * self.width..(index + 1) * self.width];
    }
}

I have tried to add an explicit lifetime but it didn’t work.

>Solution :

You should use [Letter], not &[Letter], for Output. The reference is already added in the index() method.

impl std::ops::Index<usize> for Board {
    type Output = [Letter];

    fn index(&self, index: usize) -> &Self::Output {
        return &self.board[index * self.width..(index + 1) * self.width];
    }
}