fix issue #449

Author: AllenX2018

extra/naming_strategy.go

@@ -18,7 +18,7 @@ type namingStrategyExtension struct {
 
 func (extension *namingStrategyExtension) UpdateStructDescriptor(structDescriptor *jsoniter.StructDescriptor) {
 	for _, binding := range structDescriptor.Fields {
-		if unicode.IsLower(rune(binding.Field.Name()[0])) {
+		if unicode.IsLower(rune(binding.Field.Name()[0])) || binding.Field.Name()[0] == '_'{
 			continue
 		}
 		tag, hastag := binding.Field.Tag().Lookup("json")

extra/naming_strategy_test.go

@@ -55,9 +55,11 @@ func Test_set_naming_strategy_with_private_field(t *testing.T) {
 	output, err := jsoniter.Marshal(struct {
 		UserName string
 		userId   int
+		_UserAge int
 	}{
 		UserName: "allen",
 		userId:   100,
+		_UserAge: 30,
 	})
 	should.Nil(err)
 	should.Equal(`{"user_name":"allen"}`, string(output))

reflect_extension.go

@@ -475,7 +475,7 @@ func calcFieldNames(originalFieldName string, tagProvidedFieldName string, whole
 		fieldNames = []string{tagProvidedFieldName}
 	}
 	// private?
-	isNotExported := unicode.IsLower(rune(originalFieldName[0]))
+	isNotExported := unicode.IsLower(rune(originalFieldName[0])) || originalFieldName[0] == '_'
 	if isNotExported {
 		fieldNames = []string{}
 	}

value_tests/struct_test.go

@@ -194,6 +194,11 @@ func init() {
 			C: 21,
 			d: time.NewTimer(10 * time.Second),
 		},
+		struct {
+			_UnderscoreField string
+		}{
+			"should not marshal",
+		},
 	)
 }