Add Overriders

viper.go

@@ -202,6 +202,8 @@ type Viper struct {
 	// Specific commands for ini parsing
 	iniLoadOptions ini.LoadOptions
 
+	overriders []Overrider
+
 	automaticEnvApplied bool
 	envKeyReplacer      StringReplacer
 	allowEmptyEnv       bool
@@ -224,6 +226,10 @@ type Viper struct {
 	decoderRegistry *encoding.DecoderRegistry
 }
 
+type Overrider interface {
+	Get(lowerCaseKey string) (string, bool)
+}
+
 // New returns an initialized Viper instance.
 func New() *Viper {
 	v := new(Viper)
@@ -1280,6 +1286,14 @@ func (v *Viper) find(lcaseKey string, flagDefault bool) interface{} {
 		return nil
 	}
 
+	if v.overriders != nil && len(v.overriders) != 0 {
+		for _, overrider := range v.overriders {
+			if val, ok := overrider.Get(lcaseKey); ok {
+				return val
+			}
+		}
+	}
+
 	// Env override next
 	if v.automaticEnvApplied {
 		// even if it hasn't been registered, if automaticEnv is used,
@@ -1406,6 +1420,16 @@ func (v *Viper) IsSet(key string) bool {
 	return val != nil
 }
 
+func AddOverrider(o Overrider) { v.AddOverrider(o) }
+
+func (v *Viper) AddOverrider(o Overrider) {
+	if v.overriders == nil {
+		v.overriders = []Overrider{}
+	}
+
+	v.overriders = append(v.overriders, o)
+}
+
 // AutomaticEnv makes Viper check if environment variables match any of the existing keys
 // (config, default or flags). If matching env vars are found, they are loaded into Viper.
 func AutomaticEnv() { v.AutomaticEnv() }