From 581da5dff9505e412bfe00824610b3431bf72014 Mon Sep 17 00:00:00 2001
From: Chris Broglie <cbroglie@zynga.com>
Date: Mon, 16 Mar 2015 01:29:23 -0700
Subject: [PATCH] Support decoding into reflect.Value instances

This is useful if you have a generic method which is trying to decode
a slice of structs individually. Since you can't pass an object of type
[]myStruct to a method expecting []interface{}, the only way to handle
it is to have the method signature accept just interface{}, and use
reflect to access the individual elements.
---
 mapstructure.go      | 17 ++++++++++++-----
 mapstructure_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/mapstructure.go b/mapstructure.go
index 381ba5d4..c83a8704 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -125,12 +125,15 @@ func WeakDecode(input, output interface{}) error {
 // a decoder has been returned, the same configuration must not be used
 // again.
 func NewDecoder(config *DecoderConfig) (*Decoder, error) {
-	val := reflect.ValueOf(config.Result)
-	if val.Kind() != reflect.Ptr {
-		return nil, errors.New("result must be a pointer")
+	val, ok := config.Result.(reflect.Value)
+	if !ok {
+		val = reflect.ValueOf(config.Result)
+		if val.Kind() != reflect.Ptr {
+			return nil, errors.New("result must be a pointer")
+		}
+		val = val.Elem()
 	}
 
-	val = val.Elem()
 	if !val.CanAddr() {
 		return nil, errors.New("result must be addressable (a pointer)")
 	}
@@ -159,7 +162,11 @@ func NewDecoder(config *DecoderConfig) (*Decoder, error) {
 // Decode decodes the given raw interface to the target pointer specified
 // by the configuration.
 func (d *Decoder) Decode(raw interface{}) error {
-	return d.decode("", raw, reflect.ValueOf(d.config.Result).Elem())
+	val, ok := d.config.Result.(reflect.Value)
+	if !ok {
+		val = reflect.ValueOf(d.config.Result).Elem()
+	}
+	return d.decode("", raw, val)
 }
 
 // Decodes an unknown data type into a specific reflection value.
diff --git a/mapstructure_test.go b/mapstructure_test.go
index 036e6b5f..bbc66b73 100644
--- a/mapstructure_test.go
+++ b/mapstructure_test.go
@@ -184,6 +184,33 @@ func TestDecode_Embedded(t *testing.T) {
 	}
 }
 
+func TestDecode_EmbeddedWithReflect(t *testing.T) {
+	t.Parallel()
+
+	input := map[string]interface{}{
+		"vstring": "foo",
+		"Basic": map[string]interface{}{
+			"vstring": "innerfoo",
+		},
+		"vunique": "bar",
+	}
+
+	result := make([]Embedded, 1)
+	rv := reflect.ValueOf(result)
+	err := Decode(input, rv.Index(0))
+	if err != nil {
+		t.Fatalf("got an err: %s", err.Error())
+	}
+
+	if result[0].Vstring != "innerfoo" {
+		t.Errorf("vstring value should be 'innerfoo': %#v", result[0].Vstring)
+	}
+
+	if result[0].Vunique != "bar" {
+		t.Errorf("vunique value should be 'bar': %#v", result[0].Vunique)
+	}
+}
+
 func TestDecode_EmbeddedPointer(t *testing.T) {
 	t.Parallel()