Reputation: 573
I understand some of the jank involving iterables and arrays, but clearly not enough. I want to take any amount of iterables (vectors, arrays, slices, anything implementing IntoIterator
) and provide an expected final size, and get an array (i.e. fixed-size) containing the chained values. To clarify, this is mostly for easy refactoring and function calling, so I want this utility to take ownership of the passed iterables and move all their contents into its output, such that:
let a1: u8 = [1, 2, 3];
let a2: u8 = [4, 5, 6];
let joined = join::<u8, 6>([a1, a2, ...]); // [u8; 6]
I tried implementing something with chain
, but couldn't get it to work out. I know I can do this unsafe
ly, but I'd rather avoid that if possible. Is there a way to do what I want?
My best (non-working) attempt:
fn join<T, C: IntoIterator<Item = T>, const N: usize>(iterables: Vec<C>) -> [T; N] {
let mut a = vec![].iter().chain(vec![]);
for iterable in iterables {
a = a.chain(iterable.into_iter());
}
a.collect().try_into().unwrap()
}
Upvotes: 0
Views: 318
Reputation: 573
With credit to @SvenMarnach for simplifying, this problem is neatly solved like so:
use std::convert::TryInto;
fn join<T: Clone, const N: usize>(iterables: Vec<&[T]>) -> [T; N] {
let slice = iterables.concat();
let length = slice.len();
slice.try_into()
.unwrap_or_else(|_| panic!("joined has length {}, expected {}", length, N))
}
Used like so:
fn main() {
let params1 = [1, 2, 3];
let params2 = [4, 5];
print!("sum: {}", sum_six_numbers(join(vec![¶ms1, ¶ms2])));
}
fn sum_six_numbers(ns: [u8; 5]) -> u8 {
ns.iter().sum()
}
Upvotes: 1