Add MapWithPrefix for convenience

structs.go

@@ -84,9 +84,19 @@ func (s *Struct) Map() map[string]interface{} {
 	return out
 }
 
+func (s *Struct) MapWithPrefix(prefix string) map[string]interface{} {
+	out := make(map[string]interface{})
+	s.FillMapWithPrefix(out, prefix)
+	return out
+}
+
 // FillMap is the same as Map. Instead of returning the output, it fills the
 // given map.
 func (s *Struct) FillMap(out map[string]interface{}) {
+	s.FillMapWithPrefix(out, "")
+}
+
+func (s *Struct) FillMapWithPrefix(out map[string]interface{}, prefix string) {
 	if out == nil {
 		return
 	}
@@ -134,19 +144,19 @@ func (s *Struct) FillMap(out map[string]interface{}) {
 		if tagOpts.Has("string") {
 			s, ok := val.Interface().(fmt.Stringer)
 			if ok {
-				out[name] = s.String()
+				out[prefix+name] = s.String()
 			}
 			continue
 		}
 
 		if isSubStruct && (tagOpts.Has("flatten")) {
 			if m, ok := finalVal.(map[string]interface{}); ok {
 				for k, v := range m {
-					out[k] = v
+					out[prefix+k] = v
 				}
 			}
 		} else {
-			out[name] = finalVal
+			out[prefix+name] = finalVal
 		}
 	}
 }
@@ -448,6 +458,10 @@ func Map(s interface{}) map[string]interface{} {
 	return New(s).Map()
 }
 
+func MapWithPrefix(s interface{}, prefix string) map[string]interface{} {
+	return New(s).MapWithPrefix(prefix)
+}
+
 // FillMap is the same as Map. Instead of returning the output, it fills the
 // given map.
 func FillMap(s interface{}, out map[string]interface{}) {

structs_test.go

@@ -113,6 +113,36 @@ func TestMap_Tag(t *testing.T) {
 
 }
 
+func TestMapWithPrefix_Tag(t *testing.T) {
+	var T = struct {
+		A string `structs:"x"`
+		B int    `structs:"y"`
+		C bool   `structs:"z"`
+	}{
+		A: "a-value",
+		B: 2,
+		C: true,
+	}
+
+	prefix := "p_"
+	a := MapWithPrefix(T, prefix)
+
+	inMap := func(key interface{}) bool {
+		for k := range a {
+			if reflect.DeepEqual(k, key) {
+				return true
+			}
+		}
+		return false
+	}
+
+	for _, key := range []string{"x", "y", "z"} {
+		if !inMap(prefix + key) {
+			t.Errorf("Map should have the key %v", prefix+key)
+		}
+	}
+}
+
 func TestMap_CustomTag(t *testing.T) {
 	var T = struct {
 		A string `json:"x"`