Trait Iterator not implemented for NonEmptyIterator?

[alexdewar]

I'm currently getting the warning below when using the nonempty-collections crate. If I modify my code to return an impl Iterator instead of an impl NonEmptyIterator it works fine. If you could shed any light on this that would be great. I'm happy to provide more code if that would be helpful.

    Checking muse2 v2.0.0-dev1 (/home/alex/code/MUSE_2.0)
error[E0277]: `impl nonempty_collections::NonEmptyIterator<Item = Result<_, input::InputError>> + '_` is not an iterator
   --> src/process.rs:245:19
    |
245 |     for result in read_csv(&file_path)? {
    |                   ^^^^^^^^^^^^^^^^^^^^^ `impl nonempty_collections::NonEmptyIterator<Item = Result<_, input::InputError>> + '_` is not an iterator
    |
    = help: the trait `Iterator` is not implemented for `impl nonempty_collections::NonEmptyIterator<Item = Result<_, input::InputError>> + '_`, which is required by `impl nonempty_collections::NonEmptyIterator<Item = Result<_, input::InputError>> + '_: IntoIterator`
    = note: required for `impl nonempty_collections::NonEmptyIterator<Item = Result<_, input::InputError>> + '_` to implement `IntoIterator`

[fosskers]

Hi, thanks for the report. I believe this is happening because while any specific instance of a NonEmptyIterator chain can be automatically converted into an Iterator when used in for, an opaque NonEmptyIterator cannot. There doesn't seem to be a blanket implementation that says "all NonEmptyIterators are obviously Iterators". This is something to look into.

In the meantime, you can work around the issue as you've described. Since you're consuming the entire thing in a for here, the guarantee of non-emptiness doesn't seem to matter here (without knowing more about your code).

[alexdewar]

Interesting. Thanks for your insight!

Unfortunately in my case I'd still like to be able to guarantee that my for loop runs at least once, so a NonEmptyIterator would be handy here. Still, I can work round this.