Map Sorting

[cal (Cal Stephens)]

Thanks for the input on this! The Core Team decided not to move forward with this specific
proposal. @Ben_Cohen listed a good rationale in this thread:

@Ben_Cohen

There are other examples where what is being proposed is a fairly narrow targeted addition, where what we need instead is a more holistic survey of the problem space. I would put map sorting into this bucket. It sugars some use cases, but does not address others (such as sorting by multiple criteria, or partial sorting). Ideally, when this is the case, instead of targeted proposals, there would be a full survey of the problem space from which a series of proposals fall out. This way we can be confident that the final set of APIs relating to sorting are consistent and composable because they've all been designed together, fully cover the problem space etc.

Ben did mention potential future directions for work in this space, which I agree with:

@Ben_Cohen

Our preferred approach would be to explore the space of sorting more thoroughly with an overview document that listed out a variety of use cases and user-specified optimizations (like stability or the Schwarzian transform), and a review of the facilities of other standard libraries. Out of this could hopefully come a variety of proposals, which would compose appropriately and cover all reasonable use cases.