Override slices if WithOverride is specified

issue64_test.go

@@ -0,0 +1,38 @@
+package mergo
+
+import (
+	"testing"
+)
+
+type Student struct {
+	Name  string
+	Books []string
+}
+
+var testData = []struct {
+	S1            Student
+	S2            Student
+	ExpectedSlice []string
+}{
+	{Student{"Jack", []string{"a", "B"}}, Student{"Tom", []string{"1"}}, []string{"a", "B"}},
+	{Student{"Jack", []string{"a", "B"}}, Student{"Tom", []string{}}, []string{"a", "B"}},
+	{Student{"Jack", []string{}}, Student{"Tom", []string{"1"}}, []string{"1"}},
+	{Student{"Jack", []string{}}, Student{"Tom", []string{}}, []string{}},
+}
+
+func TestIssue64MergeSliceWithOverride(t *testing.T) {
+	for _, data := range testData {
+		err := Merge(&data.S2, data.S1, WithOverride)
+		if err != nil {
+			t.Errorf("Error while merging %s", err)
+		}
+		if len(data.S2.Books) != len(data.ExpectedSlice) {
+			t.Fatalf("Got %d elements in slice, but expected %d", len(data.S2.Books), len(data.ExpectedSlice))
+		}
+		for i, val := range data.S2.Books {
+			if val != data.ExpectedSlice[i] {
+				t.Fatalf("Expected %s, but got %s while merging slice with override", data.ExpectedSlice[i], val)
+			}
+		}
+	}
+}

merge.go

@@ -130,7 +130,11 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 			}
 		}
 	case reflect.Slice:
-		dst.Set(reflect.AppendSlice(dst, src))
+		if !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) {
+			dst.Set(src)
+		} else {
+			dst.Set(reflect.AppendSlice(dst, src))
+		}
 	case reflect.Ptr:
 		fallthrough
 	case reflect.Interface: