feat(Go-Tool)：2020/11/12:新增linq包使用示例(未完成)

vendor/github.com/ahmetalpbalkan/go-linq/groupjoin.go

@@ -0,0 +1,50 @@
+package linq
+
+// GroupJoin correlates the elements of two collections based on key equality,
+// and groups the results.
+//
+// This method produces hierarchical results, which means that elements from outer query
+// are paired with collections of matching elements from inner. GroupJoin enables you
+// to base your results on a whole set of matches for each element of outer query.
+//
+// The resultSelector function is called only one time for each outer element
+// together with a collection of all the inner elements that match the outer element.
+// This differs from the Join method, in which the result selector function is invoked
+// on pairs that contain one element from outer and one element from inner.
+//
+// GroupJoin preserves the order of the elements of outer, and for each element of outer,
+// the order of the matching elements from inner.
+func (q Query) GroupJoin(
+	inner Query,
+	outerKeySelector func(interface{}) interface{},
+	innerKeySelector func(interface{}) interface{},
+	resultSelector func(outer interface{}, inners []interface{}) interface{},
+) Query {
+
+	return Query{
+		Iterate: func() Iterator {
+			outernext := q.Iterate()
+			innernext := inner.Iterate()
+
+			innerLookup := make(map[interface{}][]interface{})
+			for innerItem, ok := innernext(); ok; innerItem, ok = innernext() {
+				innerKey := innerKeySelector(innerItem)
+				innerLookup[innerKey] = append(innerLookup[innerKey], innerItem)
+			}
+
+			return func() (item interface{}, ok bool) {
+				if item, ok = outernext(); !ok {
+					return
+				}
+
+				if group, has := innerLookup[outerKeySelector(item)]; !has {
+					item = resultSelector(item, []interface{}{})
+				} else {
+					item = resultSelector(item, group)
+				}
+
+				return
+			}
+		},
+	}
+}