diff --git a/config/get.go b/config/get.go
index 2d40f87..38b053a 100644
--- a/config/get.go
+++ b/config/get.go
@@ -17,6 +17,17 @@ var (
 	boolTable   map[string]bool
 )
 
+type (
+	// StringOption defines the returned function by GetAsString.
+	StringOption func() string
+	// StringArrayOption defines the returned function by GetAsStringArray.
+	StringArrayOption func() []string
+	// IntOption defines the returned function by GetAsInt.
+	IntOption func() int64
+	// BoolOption defines the returned function by GetAsBool.
+	BoolOption func() bool
+)
+
 func getValidityFlag() *abool.AtomicBool {
 	validityFlagLock.RLock()
 	defer validityFlagLock.RUnlock()
@@ -31,7 +42,7 @@ func resetValidityFlag() {
 }
 
 // GetAsString returns a function that returns the wanted string with high performance.
-func GetAsString(name string, fallback string) func() string {
+func GetAsString(name string, fallback string) StringOption {
 	valid := getValidityFlag()
 	value := findStringValue(name, fallback)
 	return func() string {
@@ -44,7 +55,7 @@ func GetAsString(name string, fallback string) func() string {
 }
 
 // GetAsStringArray returns a function that returns the wanted string with high performance.
-func GetAsStringArray(name string, fallback []string) func() []string {
+func GetAsStringArray(name string, fallback []string) StringArrayOption {
 	valid := getValidityFlag()
 	value := findStringArrayValue(name, fallback)
 	return func() []string {
@@ -57,7 +68,7 @@ func GetAsStringArray(name string, fallback []string) func() []string {
 }
 
 // GetAsInt returns a function that returns the wanted int with high performance.
-func GetAsInt(name string, fallback int64) func() int64 {
+func GetAsInt(name string, fallback int64) IntOption {
 	valid := getValidityFlag()
 	value := findIntValue(name, fallback)
 	return func() int64 {
@@ -70,7 +81,7 @@ func GetAsInt(name string, fallback int64) func() int64 {
 }
 
 // GetAsBool returns a function that returns the wanted int with high performance.
-func GetAsBool(name string, fallback bool) func() bool {
+func GetAsBool(name string, fallback bool) BoolOption {
 	valid := getValidityFlag()
 	value := findBoolValue(name, fallback)
 	return func() bool {
diff --git a/config/registry.go b/config/registry.go
index da5ff5f..b67c981 100644
--- a/config/registry.go
+++ b/config/registry.go
@@ -14,9 +14,9 @@ const (
 	OptTypeInt         uint8 = 3
 	OptTypeBool        uint8 = 4
 
-	ExpertiseLevelUser      int8 = 1
-	ExpertiseLevelExpert    int8 = 2
-	ExpertiseLevelDeveloper int8 = 3
+	ExpertiseLevelUser      uint8 = 1
+	ExpertiseLevelExpert    uint8 = 2
+	ExpertiseLevelDeveloper uint8 = 3
 )
 
 var (