Please provide standard functions for generating immutable collections, including slices and hashmaps, safe for use as package-level members.

I think it is too late to require pointers in order to modify collections, at least within Go 1.x. We may have to superimpose a freeze() function returning an immutable, potentially type-distinct, flavor of collections.

Rust has this. Ruby has this. Haskell has this. Clojure has this. Python has third party libraries for this.

C/C++ probably require wrapper functions, meaning that developers can easily expose mutable collections without intending to.