feat: skip unexported field on readStructMetadata

add example test case

cleanenv.go

@@ -333,7 +333,10 @@ func readStructMetadata(cfgRoot interface{}) ([]structMeta, error) {
 
 			// process nested structure (except of supported ones)
 			if fld := s.Field(idx); fld.Kind() == reflect.Struct {
-
+				//skip unexported
+				if !fld.CanInterface() {
+					continue
+				}
 				// add structure to parsing stack
 				if _, found := validStructs[fld.Type()]; !found {
 					prefix, _ := fType.Tag.Lookup(TagEnvPrefix)

example_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/url"
 	"os"
+	"testing"
 
 	"github.com/ilyakaznacheev/cleanenv"
 )
@@ -271,3 +272,21 @@ func ExampleUsage() {
 	//   THREE string
 	//     	third parameter
 }
+
+func ExampleUnexportedField(t *testing.T) {
+	conf := struct {
+		Database struct {
+			Host        string `yaml:"host" env:"DB_HOST" env-description:"Database host"`
+			Port        string `yaml:"port" env:"DB_PORT" env-description:"Database port"`
+		} `yaml:"database"`
+		server struct {
+			Host string `yaml:"host" env:"SRV_HOST,HOST" env-description:"Server host" env-default:"localhost"`
+			Port string `yaml:"port" env:"SRV_PORT,PORT" env-description:"Server port" env-default:"8080"`
+		} `yaml:"server"`
+	}{}
+
+	if err := cleanenv.ReadConfig("example/simple_config/config.yml", &conf); err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("%+v", conf)
+}