In particular, the biggest pain point for the lack of anonymized return types won't be the use case mentioned in that SO thread (which is heinously ugly and leaks implementation details, but at least it's possible), but will rather be the fact that without anonymized return types it will be impossible for a function to construct a closure and then return that closure without stuffing it into a box (though note that it will still be possible for functions to return unboxed closures if it accepted that closure as a parameter to the function).