Merge pull request #67 from Indivizo/66-private-slice

Fix merging private slices (issue 66)

issue66_test.go

@@ -0,0 +1,34 @@
+package mergo
+
+import (
+	"testing"
+)
+
+type PrivateSliceTest66 struct {
+	PublicStrings []string
+
+	privateStrings []string
+}
+
+func TestPrivateSlice(t *testing.T) {
+	p1 := PrivateSliceTest66{
+		PublicStrings:  []string{"one", "two", "three"},
+		privateStrings: []string{"four", "five"},
+	}
+
+	p2 := PrivateSliceTest66{
+		PublicStrings: []string{"six", "seven"},
+	}
+
+	if err := Merge(&p1, p2); err != nil {
+		t.Fatalf("Error during the merge: %v", err)
+	}
+
+	if len(p1.PublicStrings) != 5 {
+		t.Error("5 elements should be in 'PublicStrings' field")
+	}
+
+	if len(p1.privateStrings) != 2 {
+		t.Error("2 elements should be in 'privateStrings' field")
+	}
+}

merge.go

@@ -131,6 +131,9 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int, co
 			}
 		}
 	case reflect.Slice:
+		if !dst.CanSet() {
+			break
+		}
 		if !isEmptyValue(src) && (overwrite || isEmptyValue(dst)) {
 			dst.Set(src)
 		} else {