From 6d96b16143c37dc3b735068c55154121d09921a6 Mon Sep 17 00:00:00 2001
From: Kolbe Kegel <kolbe>
Date: Tue, 22 Aug 2017 23:35:11 -0700
Subject: [PATCH] Added UnmarshalKeyExact() as well as non-method
 UnmarshalExact().

---
 viper.go | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/viper.go b/viper.go
index 2a221e5..4b93427 100644
--- a/viper.go
+++ b/viper.go
@@ -768,6 +768,7 @@ func decode(input interface{}, config *mapstructure.DecoderConfig) error {
 
 // UnmarshalExact unmarshals the config into a Struct, erroring if a field is nonexistent
 // in the destination struct.
+func UnmarshalExact(rawVal interface{}) error { return v.UnmarshalExact(rawVal) }
 func (v *Viper) UnmarshalExact(rawVal interface{}) error {
 	config := defaultDecoderConfig(rawVal)
 	config.ErrorUnused = true
@@ -782,6 +783,23 @@ func (v *Viper) UnmarshalExact(rawVal interface{}) error {
 
 	return nil
 }
+// UnmarshalKeyExact takes a single key and unmarshals it into a Struct, erroring if a field
+// is nonexistent in the destination struct.
+func UnmarshalKeyExact(key string, rawVal interface{}) error { return v.UnmarshalKeyExact(key, rawVal) }
+func (v *Viper) UnmarshalKeyExact(key string, rawVal interface{}) error {
+	config := defaultDecoderConfig(rawVal)
+	config.ErrorUnused = true
+
+	err := decode(v.Get(key), config)
+
+	if err != nil {
+		return err
+	}
+
+	v.insensitiviseMaps()
+
+	return nil
+}
 
 // BindPFlags binds a full flag set to the configuration, using each flag's long
 // name as the config key.