github.com/deckarep/GoLang-set (go): Package mapset implements a simple and generic set collection. Items stored within it are unordered and unique. It supports typical set operations: membership testing, intersection, union, difference, symmetric difference and cloning.  Package mapset provides two implementations of the Set interface. The default implementation is safe for concurrent access, but a non-thread-safe implementation is also provided for programs that can benefit from the slight speed improvement and that can enforce mutual exclusion through other means.
Keywords: concurrency|datastructures|generics|go|golang|set|threadsafe