Unless you want to implement that on top of your custom structure, like, for example, b-tree. Then you either need to write N different implementations for each separate tree or you need to use `interface{}`.
Go has the most useful containers built in. Most code I write doesn't need custom containers, even in languages with templates (I write far more C++ and Java than Go) -- so I find that I don't miss them much when I spend time in Gopherspace.
I suppose it's not sorted or concurrent-safe?
`map[T]struct{}` is only a type, it's not an implementation. You still need a handful of methods, that might be named inconsistently in each implementation by different developers. I will be happy when I never have to think about this again
Set storage is not really the concern here, it's the set-theoretic operations which make sets useful (generally speaking, there are cases where all you need is the set being a set e.g. deduplication).
So I wouldn't be surprised that GP found several different implementations of union, intersection, difference, symmetric difference, subset, superset, …