fix: return a new slice on funk.Uniq and avoid mutate input (fixes #87)

Author: thoas

transform.go

@@ -313,6 +313,8 @@ func Uniq(in interface{}) interface{} {
 	if kind == reflect.Array || kind == reflect.Slice {
 		length := value.Len()
 
+		result := makeSlice(value, 0)
+
 		seen := make(map[interface{}]bool, length)
 		j := 0
 
@@ -325,14 +327,11 @@ func Uniq(in interface{}) interface{} {
 			}
 
 			seen[v] = true
-			// Edits the original to add only unique elements.
-			// If there are j unique elements in the input, it will be modified to contain the unique elements from
-			// from index 0 through j
-			value.Index(j).Set(val)
+			result = reflect.Append(result, val)
 			j++
 		}
 
-		return value.Slice(0, j).Interface()
+		return result.Interface()
 	}
 
 	panic(fmt.Sprintf("Type %s is not supported by Uniq", valueType.String()))

transform_test.go

@@ -134,13 +134,15 @@ func TestReverse(t *testing.T) {
 }
 
 func TestUniq(t *testing.T) {
-	results := Uniq([]int{0, 1, 1, 2, 3, 0, 0, 12})
-
 	is := assert.New(t)
 
+	results := Uniq([]int{0, 1, 1, 2, 3, 0, 0, 12})
 	is.Len(results, 5)
-
 	is.Equal(results, []int{0, 1, 2, 3, 12})
+
+	results = Uniq([]string{"foo", "bar", "foo", "bar", "bar"})
+	is.Len(results, 2)
+	is.Equal(results, []string{"foo", "bar"})
 }
 
 func TestConvertSlice(t *testing.T) {

utils.go

@@ -1,6 +1,8 @@
 package funk
 
-import "reflect"
+import (
+	"reflect"
+)
 
 func equal(expected, actual interface{}) bool {
 	if expected == nil || actual == nil {