Support unmarshal custom type (#127)

aconfig_test.go

@@ -2,6 +2,7 @@ package aconfig
 
 import (
 	"embed"
+	"fmt"
 	"io/ioutil"
 	"net/url"
 	"os"
@@ -11,6 +12,25 @@ import (
 	"time"
 )
 
+type LogLevel int8
+
+func (l *LogLevel) UnmarshalText(text []byte) error {
+	switch string(text) {
+	case "debug":
+		*l = -1
+	case "info":
+		*l = 0
+	case "warn":
+		*l = 1
+	case "error":
+		*l = 2
+	default:
+		return fmt.Errorf("unknown log level: %s", text)
+	}
+
+	return nil
+}
+
 func TestDefaults(t *testing.T) {
 	var cfg TestConfig
 	loader := LoaderFor(&cfg, Config{
@@ -71,6 +91,8 @@ func TestDefaults_AllTypes(t *testing.T) {
 
 		Dur  time.Duration `default:"1h2m3s"`
 		Time time.Time     `default:"2000-04-05 10:20:30 +0000 UTC"`
+
+		Level LogLevel `default:"warn"`
 	}
 
 	var cfg AllTypesConfig
@@ -101,6 +123,7 @@ func TestDefaults_AllTypes(t *testing.T) {
 		Dur:     time.Hour + 2*time.Minute + 3*time.Second,
 		// TODO
 		// Time :2000-04-05 10:20:30 +0000 UTC,
+		Level: LogLevel(1),
 	}
 
 	if got := cfg; got != want {

reflection.go

@@ -1,6 +1,7 @@
 package aconfig
 
 import (
+	"encoding"
 	"fmt"
 	"reflect"
 	"strconv"
@@ -158,6 +159,11 @@ func (l *Loader) setFieldData(field *fieldData, value interface{}) error {
 		return nil
 	}
 
+	pv := field.value.Addr().Interface()
+	if v, ok := pv.(encoding.TextUnmarshaler); ok {
+		return v.UnmarshalText([]byte(fmt.Sprint(value)))
+	}
+
 	switch kind := field.value.Type().Kind(); kind {
 	case reflect.Bool:
 		return l.setBool(field, fmt.Sprint(value))