We have to be careful when using impl trait in return position in public APIs. The opaqueness means that the consumer of the API cannot name the type and canno

We have to be careful when using impl trait in return position in public APIs. The opaqueness means that the consumer of the API cannot name the type and cannot store it inside of a struct (without making it generic (moving the issue one level higher), or boxing). I will consider this feature complete once we get the ability to name these opaque types, via a type alias impl trait.