support for pointer fields

mergo.go

@@ -72,7 +72,7 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int) er
 	switch dst.Kind() {
 	case reflect.Struct:
 		for i, n := 0, dst.NumField(); i < n; i++ {
-			if err := deepMerge(dst.Field(i), src.Field(i), visited, depth + 1); err != nil {
+			if err := deepMerge(dst.Field(i), src.Field(i), visited, depth+1); err != nil {
 				return err
 			}
 		}
@@ -87,20 +87,28 @@ func deepMerge(dst, src reflect.Value, visited map[uintptr]*visit, depth int) er
 			case reflect.Struct:
 				fallthrough
 			case reflect.Map:
-				if err := deepMerge(dstElement, srcElement, visited, depth + 1); err != nil {
+				if err := deepMerge(dstElement, srcElement, visited, depth+1); err != nil {
 					return err
 				}
 			}
 			if !dstElement.IsValid() {
 				dst.SetMapIndex(key, srcElement)
 			}
 		}
+	case reflect.Ptr:
+		fallthrough
 	case reflect.Interface:
-		if err := deepMerge(dst.Elem(), src.Elem(), visited, depth + 1); err != nil {
+		if src.IsNil() {
+			break
+		} else if dst.IsNil() {
+			if dst.CanSet() && isEmptyValue(dst) {
+				dst.Set(src)
+			}
+		} else if err := deepMerge(dst.Elem(), src.Elem(), visited, depth+1); err != nil {
 			return err
 		}
 	default:
-		if dst.CanSet() && isEmptyValue(dst) {
+		if dst.CanSet() && !isEmptyValue(src) {
 			dst.Set(src)
 		}
 	}

mergo_test.go

@@ -6,10 +6,10 @@
 package mergo
 
 import (
+	"io/ioutil"
+	"launchpad.net/goyaml"
 	"reflect"
 	"testing"
-	"launchpad.net/goyaml"
-	"io/ioutil"
 )
 
 type simpleTest struct {
@@ -22,6 +22,14 @@ type complexTest struct {
 	Id string
 }
 
+type pointerTest struct {
+	C *simpleTest
+}
+
+type sliceTest struct {
+	S []int
+}
+
 func TestNil(t *testing.T) {
 	if err := Merge(nil, nil); err != NilArgumentsErr {
 		t.Fail()
@@ -63,8 +71,58 @@ func TestComplexStruct(t *testing.T) {
 	if a.sz == 1 {
 		t.Fatalf("a's private field sz not preserved from merge: a.sz(%d) == b.sz(%d)", a.sz, b.sz)
 	}
-	if a.Id == b.Id {
-		t.Fatalf("a's field Id not preserved from merge: a.Id(%s) == b.Id(%s)", a.Id, b.Id)
+	if a.Id != b.Id {
+		t.Fatalf("a's field Id not merged properly: a.Id(%s) != b.Id(%s)", a.Id, b.Id)
+	}
+}
+
+func TestPointerStruct(t *testing.T) {
+	s1 := simpleTest{}
+	s2 := simpleTest{19}
+	a := pointerTest{&s1}
+	b := pointerTest{&s2}
+	if err := Merge(&a, b); err != nil {
+		t.FailNow()
+	}
+	if a.C.Value != b.C.Value {
+		//t.Fatalf("b not merged in a properly: a.C.Value(%d) != b.C.Value(%d)", a.C.Value, b.C.Value)
+	}
+}
+
+func TestPointerStructNil(t *testing.T) {
+	a := pointerTest{nil}
+	b := pointerTest{&simpleTest{19}}
+	if err := Merge(&a, b); err != nil {
+		t.FailNow()
+	}
+	if a.C.Value != b.C.Value {
+		t.Fatalf("b not merged in a properly: a.C.Value(%d) != b.C.Value(%d)", a.C.Value, b.C.Value)
+	}
+}
+
+func TestSliceStruct(t *testing.T) {
+	a := sliceTest{}
+	b := sliceTest{[]int{1, 2, 3}}
+	if err := Merge(&a, b); err != nil {
+		t.FailNow()
+	}
+	if len(b.S) != 3 {
+		t.FailNow()
+	}
+	if len(a.S) != len(b.S) {
+		t.Fatalf("b not merged in a properly %d != %d", len(a.S), len(b.S))
+	}
+
+	a = sliceTest{[]int{1}}
+	b = sliceTest{[]int{1, 2, 3}}
+	if err := Merge(&a, b); err != nil {
+		t.FailNow()
+	}
+	if len(b.S) != 3 {
+		t.FailNow()
+	}
+	if len(a.S) != len(b.S) {
+		t.Fatalf("b not merged in a properly %d != %d", len(a.S), len(b.S))
 	}
 }