feat: variation of PR mitchellh#294

mapstructure.go

@@ -3,9 +3,9 @@
 // into a native Go structure.
 //
 // The Go structure can be arbitrarily complex, containing slices,
-// other structs, etc. and the decoder will properly decode nested
+// other structs, etc. and the Unmarshaler will properly decode nested
 // maps and so on into the proper structures in the native Go struct.
-// See the examples to see what the decoder is capable of.
+// See the examples to see what the Unmarshaler is capable of.
 //
 // The simplest function to start with is Decode.
 //
@@ -129,7 +129,7 @@
 // # Unexported fields
 //
 // Since unexported (private) struct fields cannot be set outside the package
-// where they are defined, the decoder will simply skip them.
+// where they are defined, the Unmarshaler will simply skip them.
 //
 // For this output type definition:
 //
@@ -196,7 +196,7 @@ type DecodeHookFuncKind func(reflect.Kind, reflect.Kind, interface{}) (interface
 // values.
 type DecodeHookFuncValue func(from reflect.Value, to reflect.Value) (interface{}, error)
 
-// DecoderConfig is the configuration that is used to create a new decoder
+// DecoderConfig is the configuration that is used to create a new Unmarshaler
 // and allows customization of various aspects of decoding.
 type DecoderConfig struct {
 	// DecodeHook, if set, will be called before any decoding and any
@@ -368,8 +368,8 @@ func WeakDecodeMetadata(input interface{}, output interface{}, metadata *Metadat
 	return decoder.Decode(input)
 }
 
-// NewDecoder returns a new decoder for the given configuration. Once
-// a decoder has been returned, the same configuration must not be used
+// NewDecoder returns a new Unmarshaler for the given configuration. Once
+// a Unmarshaler has been returned, the same configuration must not be used
 // again.
 func NewDecoder(config *DecoderConfig) (*Decoder, error) {
 	val := reflect.ValueOf(config.Result)
@@ -462,6 +462,13 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
 		}
 	}
 
+	if outVal.CanAddr() {
+		v := outVal.Addr()
+		if u, ok := v.Interface().(Unmarshaler); ok {
+			return u.DecodeMapstructure(input)
+		}
+	}
+
 	var err error
 	outputKind := getKind(outVal)
 	addMetaKey := true
@@ -1580,3 +1587,7 @@ func dereferencePtrToStructIfNeeded(v reflect.Value, tagName string) reflect.Val
 	}
 	return v
 }
+
+type Unmarshaler interface {
+	DecodeMapstructure(interface{}) error
+}

mapstructure_examples_test.go

@@ -293,6 +293,35 @@ func ExampleDecode_omitempty() {
 	// &map[Age:0 FirstName:Somebody]
 }
 
+type Someone struct {
+	Name string
+}
+
+func (p *Someone) DecodeMapstructure(v interface{}) error {
+	if name, ok := v.(string); ok {
+		p.Name = name
+		return nil
+	}
+	return fmt.Errorf("undecipherable name")
+}
+
+func ExampleDecode_custom_decoder_type() {
+	type Profile struct {
+		Friends []Someone
+	}
+	input := map[string]interface{}{
+		"friends": []string{"Mitchell"},
+	}
+	var result Profile
+	err := Decode(input, &result)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("%#v", result)
+	// Output:
+	// mapstructure.Profile{Friends:[]mapstructure.Someone{mapstructure.Someone{Name:"Mitchell"}}}
+}
+
 func ExampleDecode_decodeHookFunc() {
 	type PersonLocation struct {
 		Latitude   float64