Returning to an old hobbyhorse: Migrating higher order function names to comply with API guidelines

[Karl]

@Chris_Lattner3

We should also consider adding the mutating form versions at the same time.

The topic of an in-place map/mutating forEach has come up many times before. My understand is that we've moved away from that model and now we hope that the ownership model will solve this.

@Joe_Groff

It’s worth noting that, with more of the ownership model fleshed out, map itself could get most of the in-place-modification optimization benefit from consuming its self argument and having the map closure consume its argument as well. This would allow a map of a uniquely-referenced value to reuse the value’s buffer, possibly even while changing the type, as long as the buffer is large enough to hold the resulting array.

I can't remember the last time we introduced an in-place mutating algorithm in the standard library -- even CollectionDifference doesn't let you apply a diff in-place.