How can I construct and pass an iterator of iterators?

Question

I am trying to grok Rust by implementing simple algorithms in it. I managed to make a generic merge_sorted, which ended up having the following signature:

Answer 1

Vec::iter borrows the items it contains, so you are iterating over borrowed iterators (&std::slice::Iter) that do not implement Iterator. To consume a vector in order to have the ownership of the items, you must call Vec::into_iter:

fn main() {
    let v1 = vec![1, 2];
    let vectors = vec![v1.iter()]; // You can use `into_iter` there to iterate over ints.
    merge_sorted(vectors.into_iter());
}

You can also require IntoIterators that can make easier the usage of your API:

fn merge_sorted<IterT, IterIterT, T: Ord>(mut arrays: IterIterT) -> Vec<T>
where
    IterT: IntoIterator<Item = T>,
    IterIterT: IntoIterator<Item = IterT>,
{
    panic!();
}

fn main() {
    let v1 = vec![1, 2];
    let vectors = vec![v1];
    merge_sorted(vectors);
}