They could be implemented as builtins, like channels, slices, and maps were. Though what's really missing is generic set functions, and a decision as to which

They could be implemented as builtins, like channels, slices, and maps were. Though what's really missing is generic set functions, and a decision as to which "hashmap shape" is the blessed set (between map[T]struct{} and map[T]bool), a "set" builtin can just be an alias to that in the same way "any" is an alias for "interface{}".