feat: Add Union method and typesafe UnionStringMap

union.go

@@ -0,0 +1,67 @@
+package funk
+
+import (
+	"reflect"
+)
+
+// Union returns the union between two collections.
+func Union(collections ...interface{}) interface{} {
+	// shortcut zero/single argument
+	if len(collections) == 0 {
+		return nil
+	} else if len(collections) == 1 {
+		return collections[0]
+	}
+
+	if !IsIteratee(collections[0]) {
+		panic("Parameter must be a collection")
+	}
+
+	cType := reflect.TypeOf(collections[0])
+	zLen := 0
+
+	for i, x := range collections {
+		xValue := reflect.ValueOf(x)
+		xType := xValue.Type()
+		if i > 0 && NotEqual(cType, xType) {
+			panic("Parameters must have the same type")
+		}
+
+		zLen += xValue.Len()
+	}
+
+	if cType.Kind() == reflect.Map {
+		zType := reflect.MapOf(cType.Key(), cType.Elem())
+		zMap := reflect.MakeMap(zType)
+
+		for _, x := range collections {
+			xIter := reflect.ValueOf(x).MapRange()
+			for xIter.Next() {
+				zMap.SetMapIndex(xIter.Key(), xIter.Value())
+			}
+		}
+
+		return zMap.Interface()
+	} else {
+		zType := reflect.SliceOf(cType.Elem())
+		zSlice := reflect.MakeSlice(zType, 0, 0)
+
+		for _, x := range collections {
+			xValue := reflect.ValueOf(x)
+			zSlice = reflect.AppendSlice(zSlice, xValue)
+		}
+
+		return zSlice.Interface()
+	}
+}
+
+// UnionStringMap returns the union between multiple string maps
+func UnionStringMap(x ...map[string]string) map[string]string {
+	zMap := map[string]string{}
+	for _, xMap := range x {
+		for k, v := range xMap {
+			zMap[k] = v
+		}
+	}
+	return zMap
+}

union_test.go

@@ -0,0 +1,34 @@
+package funk
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnion(t *testing.T) {
+	is := assert.New(t)
+
+	r := Union([]int{1, 2, 3, 4}, []int{2, 4, 6})
+	is.Equal(r, []int{1, 2, 3, 4, 2, 4, 6})
+
+	r = Union(map[int]int{1: 1, 2: 2}, map[int]int{1: 0, 3: 3})
+	is.Equal(r, map[int]int{1: 0, 2: 2, 3: 3})
+}
+
+func TestUnionShortcut(t *testing.T) {
+	is := assert.New(t)
+
+	r := Union(nil)
+	is.Nil(r)
+
+	r = Union([]int{1, 2})
+	is.Equal(r, []int{1, 2})
+}
+
+func TestUnionStringMap(t *testing.T) {
+	is := assert.New(t)
+
+	r := Union(map[string]string{"a": "a", "b": "b"}, map[string]string{"a": "z", "z": "a"}, map[string]string{"z": "z"})
+	is.Equal(r, map[string]string{"a": "z", "b": "b", "z": "z"})
+}