`IntoIter` type when the `into_iter` is a bunch of `values`, `map`, `flatten` etc. calls?

help
1

I'm trying to implement IntoIterator for my type and I'm not sure how to specify the associated type IntoIter.

The into_iter function body looks like this:

self.set.values().map(TraitPreds::iter).flatten()

So the concrete iterator type is a complex type and I don't want to figure it out myself. Normally in a non-trait method I'd use impl Iterator<Item = ...> + '_, but that's not valid when specifying associated types.

I'd normally not care and just implement non-trait into_iter/iters and use them explicitly in the loops, but I have code that iterates the previous version of this type currently and I'm trying to be somewhat backwards compatible to keep the diff small.

Is there a trick to this? Do I have to manually figure out the concrete iterator type here?

2

on stable, if you don't wnat to box the result, I'm afraid you'll have to figure out the full type name.

3

On nightly?

4

on nightly, there's #![feature(impl_trait_in_assoc_type)]:

impl IntoIterator for MyType {
    type Item = i64;
    type IntoIter = impl Iterator<Item = Self::Item>;
    fn into_iter(self) -> Self::IntoIter {
        self.0.into_iter().map(|x| 2 * x as i64)
    }
}

playground:

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