[esprehn]

That's easily resolved with an ensureCapacity(size) method, or the other way around with shrinkToFit(size).

maps being magic without a real interface means exposing new API surface is difficult though.

[morelisp]

A few times I have wished for a way to grow maps, but generally to shrink maps I don't think there's any big advantage to a built-in rather than your own function making a new one. (It would only cover the case where you know you want to shrink but don't know if you need to shrink because you don't know how many elements you removed or overestimated by, which I think is pretty unusual.)

[tapirl]

Personally, I am not against the proposal to add a "shrink(aMapOrSlice)` builtin function. In fact, there are more builtin functions on my wish list, such as "concat(slices)" and "decap(aSlice)".

It is just that the Go core team have their own philosophy.