add gem analyzer

internal/stringset.go

@@ -0,0 +1,28 @@
+package internal
+
+type Set map[string]struct{}
+
+func NewStringSet() Set {
+	return make(Set)
+}
+
+func NewStringSetFromSlice(start []string) Set {
+	ret := make(Set)
+	for _, s := range start {
+		ret.Add(s)
+	}
+	return ret
+}
+
+func (s Set) Add(i string) {
+	s[i] = struct{}{}
+}
+
+func (s Set) Remove(i string) {
+	delete(s, i)
+}
+
+func (s Set) Contains(i string) bool {
+	_, ok := s[i]
+	return ok
+}