feat(unmarshaler): add interface so that children nodes can define custom unmarshal behavior

Author: pkarakal

mapstructure.go

@@ -301,6 +301,10 @@ type Metadata struct {
 	Unset []string
 }
 
+type Unmarshaler interface {
+	UnmarshalMapStructure(interface{}) error
+}
+
 // Decode takes an input structure and uses reflection to translate it to
 // the output structure. output must be a pointer to a map or struct.
 func Decode(input interface{}, output interface{}) error {
@@ -453,6 +457,12 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
 		return nil
 	}
 
+	if outVal.CanAddr() {
+		if v, ok := outVal.Addr().Interface().(Unmarshaler); ok {
+			return v.UnmarshalMapStructure(input)
+		}
+	}
+
 	if d.config.DecodeHook != nil {
 		// We have a DecodeHook, so let's pre-process the input.
 		var err error

mapstructure_examples_test.go

@@ -2,6 +2,7 @@ package mapstructure
 
 import (
 	"fmt"
+	"strconv"
 )
 
 func ExampleDecode() {
@@ -289,3 +290,37 @@ func ExampleDecode_omitempty() {
 	// Output:
 	// &map[Age:0 FirstName:Somebody]
 }
+
+type CustomUnmarshaler struct {
+	ID int64
+}
+
+func (c *CustomUnmarshaler) UnmarshalMapStructure(v interface{}) error {
+	if sid, ok := v.(string); ok {
+		id, err := strconv.ParseInt(sid, 10, 64)
+		if err != nil {
+			return fmt.Errorf("error converting id to int, %v", err)
+		}
+		c.ID = id
+		return nil
+
+	}
+	return fmt.Errorf("error unmarshaling")
+}
+
+func ExampleDecode_structImplementsUnmarshalerInterface() {
+	type Custom struct {
+		Unmarshalers []CustomUnmarshaler
+	}
+	input := map[string]interface{}{
+		"unmarshalers": []string{"123456"},
+	}
+	var result Custom
+	err := Decode(input, &result)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("%#v", result)
+	// Output:
+	// mapstructure.Custom{Unmarshalers:[]mapstructure.CustomUnmarshaler{mapstructure.CustomUnmarshaler{ID:123456}}}
+}