将对元组的引用迭代器解压缩为两个引用集合

Question

I have an Iterator<Item = &(T, U)> over a slice &[(T, U)] . I'd like to unzip this iterator into its components (ie obtain (Vec<&T>, Vec<&U>) ).

Rust provides unzip functionality through the .unzip() method on Interator :

points.iter().unzip()

Unfortunately, this doesn't work as-is because .unzip() expects the type of the iterator's item to be a tuple; mine is a reference to a tuple.

To fix this, I tried to write a function which converts between a reference to a tuple and a tuple of references:

fn distribute_ref<'a, T, U>(x: &'a (T, U)) -> (&'a T, &'a U) {
    (&x.0, &x.1)
}

I can then map over the resulting iterator to get something .unzip() can handle:

points.iter().map(distribute_ref).unzip()

This works now, but I this feels a bit strange. In particular, distribute_ref seems like a fairly simple operation that would be provided by the Rust standard library. I'm guessing it either is and I can't find it, or I'm not approaching this the right way.

Is there a better way to do this?

Answer 1

Is there a better way to do this?

"Better" is a bit subjective. You can make your function shorter:

fn distribute_ref<T, U>(x: &(T, U)) -> (&T, &U) {
    (&x.0, &x.1)
}

Lifetime elision allows to omit lifetime annotations in this case.

You can use a closure to do the same thing:

points.iter().map(|&(ref a, ref b)| (a, b)).unzip()

Depending on the task it can be sufficient to clone the data. Especially in this case, as reference to u8 takes 4 or 8 times more space than u8 itself.

points().iter().cloned().unzip()