Add user-defined tag naming

README.md

@@ -24,6 +24,7 @@ Initialize structs with default values
 - Recursively initializes fields in a struct
 - Dynamically sets default values by [`defaults.Setter`](./setter.go) interface
 - Preserves non-initial values from being reset with a default value
+- User-Definable tag name
 
 
 Usage
@@ -42,6 +43,9 @@ import (
 
 type Gender string
 
+// Optionally use a different tag name globally.
+//defaults.TagName = "my_custom_tag"
+
 type Sample struct {
 	Name    string `default:"John Smith"`
 	Age     int    `default:"27"`
@@ -83,6 +87,12 @@ func main() {
 	if err := defaults.Set(obj); err != nil {
 		panic(err)
 	}
+	// Or with a specific tag name (without setting defaults.TagName globally):
+	/*
+	if err := defaults.SetWithTag(obj, "some_tag_name"); err != nil {
+	    panic(err)
+	}
+	*/
 
 	out, err := json.MarshalIndent(obj, "", "	")
 	if err != nil {

defaults.go

@@ -6,17 +6,23 @@
 	"errors"
 	"reflect"
 	"strconv"
+	"strings"
 	"time"
 )
 
 var (
+	errInvalidTag  = errors.New("invalid tag name")
 	errInvalidType = errors.New("not a struct pointer")
 )
 
 const (
 	fieldName = "default"
 )
 
+var (
+	TagName string = fieldName
+)
+
 // Set initializes members in a struct referenced by a pointer.
 // Maps and slices are initialized by `make` and other primitive types are set with default values.
 // `ptr` should be a struct pointer
@@ -25,6 +31,40 @@
 		return errInvalidType
 	}
 
+	if strings.TrimSpace(TagName) == "" {
+		return errInvalidTag
+	}
+
+	v := reflect.ValueOf(ptr).Elem()
+	t := v.Type()
+
+	if t.Kind() != reflect.Struct {
+		return errInvalidType
+	}
+
+	for i := 0; i < t.NumField(); i++ {
+		if defaultVal := t.Field(i).Tag.Get(TagName); defaultVal != "-" {
+			if err := setField(v.Field(i), defaultVal); err != nil {
+				return err
+			}
+		}
+	}
+	callSetter(ptr)
+	return nil
+}
+
+// SetWithTag initializes members in a struct referenced by a pointer using an explicit tag name.
+// Maps and slices are initialized by `make` and other primitive types are set with default values.
+// `ptr` should be a struct pointer
+func SetWithTag(ptr interface{}, runtimeTag string) error {
+	if reflect.TypeOf(ptr).Kind() != reflect.Ptr {
+		return errInvalidType
+	}
+
+	if strings.TrimSpace(runtimeTag) == "" {
+		return errInvalidTag
+	}
+
 	v := reflect.ValueOf(ptr).Elem()
 	t := v.Type()
 
@@ -33,7 +73,7 @@
 	}
 
 	for i := 0; i < t.NumField(); i++ {
-		if defaultVal := t.Field(i).Tag.Get(fieldName); defaultVal != "-" {
+		if defaultVal := t.Field(i).Tag.Get(runtimeTag); defaultVal != "-" {
 			if err := setField(v.Field(i), defaultVal); err != nil {
 				return err
 			}