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mirror of https://github.com/json-iterator/go.git synced 2024-11-24 08:22:14 +02:00
json-iterator/feature_reflect.go
Oleg Shaldybin ae57d167e8 Fix custom marshaler for enum types
When MarshalJSON was defined on a pointer receiver custom enum type
marshaling/unmarshaling was panicing since the underlying primitive type
was treated as a pointer.

Since method set for pointer receivers includes value receiver methods
we don't really need optionalEncoder and can just use marshalEncoder
directly.
2017-09-14 23:26:12 -07:00

704 lines
20 KiB
Go

package jsoniter
import (
"encoding"
"encoding/json"
"fmt"
"reflect"
"time"
"unsafe"
)
// ValDecoder is an internal type registered to cache as needed.
// Don't confuse jsoniter.ValDecoder with json.Decoder.
// For json.Decoder's adapter, refer to jsoniter.AdapterDecoder(todo link).
//
// Reflection on type to create decoders, which is then cached
// Reflection on value is avoided as we can, as the reflect.Value itself will allocate, with following exceptions
// 1. create instance of new value, for example *int will need a int to be allocated
// 2. append to slice, if the existing cap is not enough, allocate will be done using Reflect.New
// 3. assignment to map, both key and value will be reflect.Value
// For a simple struct binding, it will be reflect.Value free and allocation free
type ValDecoder interface {
Decode(ptr unsafe.Pointer, iter *Iterator)
}
// ValEncoder is an internal type registered to cache as needed.
// Don't confuse jsoniter.ValEncoder with json.Encoder.
// For json.Encoder's adapter, refer to jsoniter.AdapterEncoder(todo godoc link).
type ValEncoder interface {
IsEmpty(ptr unsafe.Pointer) bool
Encode(ptr unsafe.Pointer, stream *Stream)
EncodeInterface(val interface{}, stream *Stream)
}
type checkIsEmpty interface {
IsEmpty(ptr unsafe.Pointer) bool
}
// WriteToStream the default implementation for TypeEncoder method EncodeInterface
func WriteToStream(val interface{}, stream *Stream, encoder ValEncoder) {
e := (*emptyInterface)(unsafe.Pointer(&val))
if e.word == nil {
stream.WriteNil()
return
}
if reflect.TypeOf(val).Kind() == reflect.Ptr {
encoder.Encode(unsafe.Pointer(&e.word), stream)
} else {
encoder.Encode(e.word, stream)
}
}
var jsonNumberType reflect.Type
var jsoniterNumberType reflect.Type
var jsonRawMessageType reflect.Type
var jsoniterRawMessageType reflect.Type
var anyType reflect.Type
var marshalerType reflect.Type
var unmarshalerType reflect.Type
var textMarshalerType reflect.Type
var textUnmarshalerType reflect.Type
func init() {
jsonNumberType = reflect.TypeOf((*json.Number)(nil)).Elem()
jsoniterNumberType = reflect.TypeOf((*Number)(nil)).Elem()
jsonRawMessageType = reflect.TypeOf((*json.RawMessage)(nil)).Elem()
jsoniterRawMessageType = reflect.TypeOf((*RawMessage)(nil)).Elem()
anyType = reflect.TypeOf((*Any)(nil)).Elem()
marshalerType = reflect.TypeOf((*json.Marshaler)(nil)).Elem()
unmarshalerType = reflect.TypeOf((*json.Unmarshaler)(nil)).Elem()
textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
textUnmarshalerType = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
}
type optionalDecoder struct {
valueType reflect.Type
valueDecoder ValDecoder
}
func (decoder *optionalDecoder) Decode(ptr unsafe.Pointer, iter *Iterator) {
if iter.ReadNil() {
*((*unsafe.Pointer)(ptr)) = nil
} else {
if *((*unsafe.Pointer)(ptr)) == nil {
//pointer to null, we have to allocate memory to hold the value
value := reflect.New(decoder.valueType)
newPtr := extractInterface(value.Interface()).word
decoder.valueDecoder.Decode(newPtr, iter)
*((*uintptr)(ptr)) = uintptr(newPtr)
} else {
//reuse existing instance
decoder.valueDecoder.Decode(*((*unsafe.Pointer)(ptr)), iter)
}
}
}
type deferenceDecoder struct {
// only to deference a pointer
valueType reflect.Type
valueDecoder ValDecoder
}
func (decoder *deferenceDecoder) Decode(ptr unsafe.Pointer, iter *Iterator) {
if *((*unsafe.Pointer)(ptr)) == nil {
//pointer to null, we have to allocate memory to hold the value
value := reflect.New(decoder.valueType)
newPtr := extractInterface(value.Interface()).word
decoder.valueDecoder.Decode(newPtr, iter)
*((*uintptr)(ptr)) = uintptr(newPtr)
} else {
//reuse existing instance
decoder.valueDecoder.Decode(*((*unsafe.Pointer)(ptr)), iter)
}
}
type optionalEncoder struct {
valueEncoder ValEncoder
}
func (encoder *optionalEncoder) Encode(ptr unsafe.Pointer, stream *Stream) {
if *((*unsafe.Pointer)(ptr)) == nil {
stream.WriteNil()
} else {
encoder.valueEncoder.Encode(*((*unsafe.Pointer)(ptr)), stream)
}
}
func (encoder *optionalEncoder) EncodeInterface(val interface{}, stream *Stream) {
WriteToStream(val, stream, encoder)
}
func (encoder *optionalEncoder) IsEmpty(ptr unsafe.Pointer) bool {
if *((*unsafe.Pointer)(ptr)) == nil {
return true
}
return false
}
type placeholderEncoder struct {
cfg *frozenConfig
cacheKey reflect.Type
}
func (encoder *placeholderEncoder) Encode(ptr unsafe.Pointer, stream *Stream) {
encoder.getRealEncoder().Encode(ptr, stream)
}
func (encoder *placeholderEncoder) EncodeInterface(val interface{}, stream *Stream) {
WriteToStream(val, stream, encoder)
}
func (encoder *placeholderEncoder) IsEmpty(ptr unsafe.Pointer) bool {
return encoder.getRealEncoder().IsEmpty(ptr)
}
func (encoder *placeholderEncoder) getRealEncoder() ValEncoder {
for i := 0; i < 500; i++ {
realDecoder := encoder.cfg.getEncoderFromCache(encoder.cacheKey)
_, isPlaceholder := realDecoder.(*placeholderEncoder)
if isPlaceholder {
time.Sleep(10 * time.Millisecond)
} else {
return realDecoder
}
}
panic(fmt.Sprintf("real encoder not found for cache key: %v", encoder.cacheKey))
}
type placeholderDecoder struct {
cfg *frozenConfig
cacheKey reflect.Type
}
func (decoder *placeholderDecoder) Decode(ptr unsafe.Pointer, iter *Iterator) {
for i := 0; i < 500; i++ {
realDecoder := decoder.cfg.getDecoderFromCache(decoder.cacheKey)
_, isPlaceholder := realDecoder.(*placeholderDecoder)
if isPlaceholder {
time.Sleep(10 * time.Millisecond)
} else {
realDecoder.Decode(ptr, iter)
return
}
}
panic(fmt.Sprintf("real decoder not found for cache key: %v", decoder.cacheKey))
}
// emptyInterface is the header for an interface{} value.
type emptyInterface struct {
typ unsafe.Pointer
word unsafe.Pointer
}
// emptyInterface is the header for an interface with method (not interface{})
type nonEmptyInterface struct {
// see ../runtime/iface.go:/Itab
itab *struct {
ityp unsafe.Pointer // static interface type
typ unsafe.Pointer // dynamic concrete type
link unsafe.Pointer
bad int32
unused int32
fun [100000]unsafe.Pointer // method table
}
word unsafe.Pointer
}
// ReadVal copy the underlying JSON into go interface, same as json.Unmarshal
func (iter *Iterator) ReadVal(obj interface{}) {
typ := reflect.TypeOf(obj)
cacheKey := typ.Elem()
decoder, err := decoderOfType(iter.cfg, cacheKey)
if err != nil {
iter.Error = err
return
}
e := (*emptyInterface)(unsafe.Pointer(&obj))
decoder.Decode(e.word, iter)
}
// WriteVal copy the go interface into underlying JSON, same as json.Marshal
func (stream *Stream) WriteVal(val interface{}) {
if nil == val {
stream.WriteNil()
return
}
typ := reflect.TypeOf(val)
cacheKey := typ
encoder, err := encoderOfType(stream.cfg, cacheKey)
if err != nil {
stream.Error = err
return
}
encoder.EncodeInterface(val, stream)
}
type prefix string
func (p prefix) addToDecoder(decoder ValDecoder, err error) (ValDecoder, error) {
if err != nil {
return nil, fmt.Errorf("%s: %s", p, err.Error())
}
return decoder, err
}
func (p prefix) addToEncoder(encoder ValEncoder, err error) (ValEncoder, error) {
if err != nil {
return nil, fmt.Errorf("%s: %s", p, err.Error())
}
return encoder, err
}
func decoderOfType(cfg *frozenConfig, typ reflect.Type) (ValDecoder, error) {
cacheKey := typ
decoder := cfg.getDecoderFromCache(cacheKey)
if decoder != nil {
return decoder, nil
}
decoder = getTypeDecoderFromExtension(typ)
if decoder != nil {
cfg.addDecoderToCache(cacheKey, decoder)
return decoder, nil
}
decoder = &placeholderDecoder{cfg: cfg, cacheKey: cacheKey}
cfg.addDecoderToCache(cacheKey, decoder)
decoder, err := createDecoderOfType(cfg, typ)
for _, extension := range extensions {
decoder = extension.DecorateDecoder(typ, decoder)
}
cfg.addDecoderToCache(cacheKey, decoder)
return decoder, err
}
func createDecoderOfType(cfg *frozenConfig, typ reflect.Type) (ValDecoder, error) {
typeName := typ.String()
if typ == jsonRawMessageType {
return &jsonRawMessageCodec{}, nil
}
if typ == jsoniterRawMessageType {
return &jsoniterRawMessageCodec{}, nil
}
if typ.AssignableTo(jsonNumberType) {
return &jsonNumberCodec{}, nil
}
if typ.AssignableTo(jsoniterNumberType) {
return &jsoniterNumberCodec{}, nil
}
if typ.Implements(unmarshalerType) {
templateInterface := reflect.New(typ).Elem().Interface()
var decoder ValDecoder = &unmarshalerDecoder{extractInterface(templateInterface)}
if typ.Kind() == reflect.Ptr {
decoder = &optionalDecoder{typ.Elem(), decoder}
}
return decoder, nil
}
if reflect.PtrTo(typ).Implements(unmarshalerType) {
templateInterface := reflect.New(typ).Interface()
var decoder ValDecoder = &unmarshalerDecoder{extractInterface(templateInterface)}
return decoder, nil
}
if typ.Implements(textUnmarshalerType) {
templateInterface := reflect.New(typ).Elem().Interface()
var decoder ValDecoder = &textUnmarshalerDecoder{extractInterface(templateInterface)}
if typ.Kind() == reflect.Ptr {
decoder = &optionalDecoder{typ.Elem(), decoder}
}
return decoder, nil
}
if reflect.PtrTo(typ).Implements(textUnmarshalerType) {
templateInterface := reflect.New(typ).Interface()
var decoder ValDecoder = &textUnmarshalerDecoder{extractInterface(templateInterface)}
return decoder, nil
}
if typ.Kind() == reflect.Slice && typ.Elem().Kind() == reflect.Uint8 {
sliceDecoder, err := prefix("[slice]").addToDecoder(decoderOfSlice(cfg, typ))
if err != nil {
return nil, err
}
return &base64Codec{sliceDecoder: sliceDecoder}, nil
}
if typ.Implements(anyType) {
return &anyCodec{}, nil
}
switch typ.Kind() {
case reflect.String:
if typeName != "string" {
return decoderOfType(cfg, reflect.TypeOf((*string)(nil)).Elem())
}
return &stringCodec{}, nil
case reflect.Int:
if typeName != "int" {
return decoderOfType(cfg, reflect.TypeOf((*int)(nil)).Elem())
}
return &intCodec{}, nil
case reflect.Int8:
if typeName != "int8" {
return decoderOfType(cfg, reflect.TypeOf((*int8)(nil)).Elem())
}
return &int8Codec{}, nil
case reflect.Int16:
if typeName != "int16" {
return decoderOfType(cfg, reflect.TypeOf((*int16)(nil)).Elem())
}
return &int16Codec{}, nil
case reflect.Int32:
if typeName != "int32" {
return decoderOfType(cfg, reflect.TypeOf((*int32)(nil)).Elem())
}
return &int32Codec{}, nil
case reflect.Int64:
if typeName != "int64" {
return decoderOfType(cfg, reflect.TypeOf((*int64)(nil)).Elem())
}
return &int64Codec{}, nil
case reflect.Uint:
if typeName != "uint" {
return decoderOfType(cfg, reflect.TypeOf((*uint)(nil)).Elem())
}
return &uintCodec{}, nil
case reflect.Uint8:
if typeName != "uint8" {
return decoderOfType(cfg, reflect.TypeOf((*uint8)(nil)).Elem())
}
return &uint8Codec{}, nil
case reflect.Uint16:
if typeName != "uint16" {
return decoderOfType(cfg, reflect.TypeOf((*uint16)(nil)).Elem())
}
return &uint16Codec{}, nil
case reflect.Uint32:
if typeName != "uint32" {
return decoderOfType(cfg, reflect.TypeOf((*uint32)(nil)).Elem())
}
return &uint32Codec{}, nil
case reflect.Uintptr:
if typeName != "uintptr" {
return decoderOfType(cfg, reflect.TypeOf((*uintptr)(nil)).Elem())
}
return &uintptrCodec{}, nil
case reflect.Uint64:
if typeName != "uint64" {
return decoderOfType(cfg, reflect.TypeOf((*uint64)(nil)).Elem())
}
return &uint64Codec{}, nil
case reflect.Float32:
if typeName != "float32" {
return decoderOfType(cfg, reflect.TypeOf((*float32)(nil)).Elem())
}
return &float32Codec{}, nil
case reflect.Float64:
if typeName != "float64" {
return decoderOfType(cfg, reflect.TypeOf((*float64)(nil)).Elem())
}
return &float64Codec{}, nil
case reflect.Bool:
if typeName != "bool" {
return decoderOfType(cfg, reflect.TypeOf((*bool)(nil)).Elem())
}
return &boolCodec{}, nil
case reflect.Interface:
if typ.NumMethod() == 0 {
return &emptyInterfaceCodec{}, nil
}
return &nonEmptyInterfaceCodec{}, nil
case reflect.Struct:
return prefix(fmt.Sprintf("[%s]", typeName)).addToDecoder(decoderOfStruct(cfg, typ))
case reflect.Array:
return prefix("[array]").addToDecoder(decoderOfArray(cfg, typ))
case reflect.Slice:
return prefix("[slice]").addToDecoder(decoderOfSlice(cfg, typ))
case reflect.Map:
return prefix("[map]").addToDecoder(decoderOfMap(cfg, typ))
case reflect.Ptr:
return prefix("[optional]").addToDecoder(decoderOfOptional(cfg, typ))
default:
return nil, fmt.Errorf("unsupported type: %v", typ)
}
}
func encoderOfType(cfg *frozenConfig, typ reflect.Type) (ValEncoder, error) {
cacheKey := typ
encoder := cfg.getEncoderFromCache(cacheKey)
if encoder != nil {
return encoder, nil
}
encoder = getTypeEncoderFromExtension(typ)
if encoder != nil {
cfg.addEncoderToCache(cacheKey, encoder)
return encoder, nil
}
encoder = &placeholderEncoder{cfg: cfg, cacheKey: cacheKey}
cfg.addEncoderToCache(cacheKey, encoder)
encoder, err := createEncoderOfType(cfg, typ)
for _, extension := range extensions {
encoder = extension.DecorateEncoder(typ, encoder)
}
cfg.addEncoderToCache(cacheKey, encoder)
return encoder, err
}
func createEncoderOfType(cfg *frozenConfig, typ reflect.Type) (ValEncoder, error) {
if typ == jsonRawMessageType {
return &jsonRawMessageCodec{}, nil
}
if typ == jsoniterRawMessageType {
return &jsoniterRawMessageCodec{}, nil
}
if typ.AssignableTo(jsonNumberType) {
return &jsonNumberCodec{}, nil
}
if typ.AssignableTo(jsoniterNumberType) {
return &jsoniterNumberCodec{}, nil
}
if typ.Implements(marshalerType) {
checkIsEmpty, err := createCheckIsEmpty(typ)
if err != nil {
return nil, err
}
templateInterface := reflect.New(typ).Elem().Interface()
var encoder ValEncoder = &marshalerEncoder{
templateInterface: extractInterface(templateInterface),
checkIsEmpty: checkIsEmpty,
}
if typ.Kind() == reflect.Ptr {
encoder = &optionalEncoder{encoder}
}
return encoder, nil
}
if reflect.PtrTo(typ).Implements(marshalerType) {
checkIsEmpty, err := createCheckIsEmpty(reflect.PtrTo(typ))
if err != nil {
return nil, err
}
templateInterface := reflect.New(typ).Interface()
var encoder ValEncoder = &marshalerEncoder{
templateInterface: extractInterface(templateInterface),
checkIsEmpty: checkIsEmpty,
}
return encoder, nil
}
if typ.Implements(textMarshalerType) {
checkIsEmpty, err := createCheckIsEmpty(typ)
if err != nil {
return nil, err
}
templateInterface := reflect.New(typ).Elem().Interface()
var encoder ValEncoder = &textMarshalerEncoder{
templateInterface: extractInterface(templateInterface),
checkIsEmpty: checkIsEmpty,
}
if typ.Kind() == reflect.Ptr {
encoder = &optionalEncoder{encoder}
}
return encoder, nil
}
if typ.Kind() == reflect.Slice && typ.Elem().Kind() == reflect.Uint8 {
return &base64Codec{}, nil
}
if typ.Implements(anyType) {
return &anyCodec{}, nil
}
return createEncoderOfSimpleType(cfg, typ)
}
func createCheckIsEmpty(typ reflect.Type) (checkIsEmpty, error) {
kind := typ.Kind()
switch kind {
case reflect.String:
return &stringCodec{}, nil
case reflect.Int:
return &intCodec{}, nil
case reflect.Int8:
return &int8Codec{}, nil
case reflect.Int16:
return &int16Codec{}, nil
case reflect.Int32:
return &int32Codec{}, nil
case reflect.Int64:
return &int64Codec{}, nil
case reflect.Uint:
return &uintCodec{}, nil
case reflect.Uint8:
return &uint8Codec{}, nil
case reflect.Uint16:
return &uint16Codec{}, nil
case reflect.Uint32:
return &uint32Codec{}, nil
case reflect.Uintptr:
return &uintptrCodec{}, nil
case reflect.Uint64:
return &uint64Codec{}, nil
case reflect.Float32:
return &float32Codec{}, nil
case reflect.Float64:
return &float64Codec{}, nil
case reflect.Bool:
return &boolCodec{}, nil
case reflect.Interface:
if typ.NumMethod() == 0 {
return &emptyInterfaceCodec{}, nil
}
return &nonEmptyInterfaceCodec{}, nil
case reflect.Struct:
return &structEncoder{}, nil
case reflect.Array:
return &arrayEncoder{}, nil
case reflect.Slice:
return &sliceEncoder{}, nil
case reflect.Map:
return &mapEncoder{}, nil
case reflect.Ptr:
return &optionalEncoder{}, nil
default:
return nil, fmt.Errorf("unsupported type: %v", typ)
}
}
func createEncoderOfSimpleType(cfg *frozenConfig, typ reflect.Type) (ValEncoder, error) {
typeName := typ.String()
kind := typ.Kind()
switch kind {
case reflect.String:
if typeName != "string" {
return encoderOfType(cfg, reflect.TypeOf((*string)(nil)).Elem())
}
return &stringCodec{}, nil
case reflect.Int:
if typeName != "int" {
return encoderOfType(cfg, reflect.TypeOf((*int)(nil)).Elem())
}
return &intCodec{}, nil
case reflect.Int8:
if typeName != "int8" {
return encoderOfType(cfg, reflect.TypeOf((*int8)(nil)).Elem())
}
return &int8Codec{}, nil
case reflect.Int16:
if typeName != "int16" {
return encoderOfType(cfg, reflect.TypeOf((*int16)(nil)).Elem())
}
return &int16Codec{}, nil
case reflect.Int32:
if typeName != "int32" {
return encoderOfType(cfg, reflect.TypeOf((*int32)(nil)).Elem())
}
return &int32Codec{}, nil
case reflect.Int64:
if typeName != "int64" {
return encoderOfType(cfg, reflect.TypeOf((*int64)(nil)).Elem())
}
return &int64Codec{}, nil
case reflect.Uint:
if typeName != "uint" {
return encoderOfType(cfg, reflect.TypeOf((*uint)(nil)).Elem())
}
return &uintCodec{}, nil
case reflect.Uint8:
if typeName != "uint8" {
return encoderOfType(cfg, reflect.TypeOf((*uint8)(nil)).Elem())
}
return &uint8Codec{}, nil
case reflect.Uint16:
if typeName != "uint16" {
return encoderOfType(cfg, reflect.TypeOf((*uint16)(nil)).Elem())
}
return &uint16Codec{}, nil
case reflect.Uint32:
if typeName != "uint32" {
return encoderOfType(cfg, reflect.TypeOf((*uint32)(nil)).Elem())
}
return &uint32Codec{}, nil
case reflect.Uintptr:
if typeName != "uintptr" {
return encoderOfType(cfg, reflect.TypeOf((*uintptr)(nil)).Elem())
}
return &uintptrCodec{}, nil
case reflect.Uint64:
if typeName != "uint64" {
return encoderOfType(cfg, reflect.TypeOf((*uint64)(nil)).Elem())
}
return &uint64Codec{}, nil
case reflect.Float32:
if typeName != "float32" {
return encoderOfType(cfg, reflect.TypeOf((*float32)(nil)).Elem())
}
return &float32Codec{}, nil
case reflect.Float64:
if typeName != "float64" {
return encoderOfType(cfg, reflect.TypeOf((*float64)(nil)).Elem())
}
return &float64Codec{}, nil
case reflect.Bool:
if typeName != "bool" {
return encoderOfType(cfg, reflect.TypeOf((*bool)(nil)).Elem())
}
return &boolCodec{}, nil
case reflect.Interface:
if typ.NumMethod() == 0 {
return &emptyInterfaceCodec{}, nil
}
return &nonEmptyInterfaceCodec{}, nil
case reflect.Struct:
return prefix(fmt.Sprintf("[%s]", typeName)).addToEncoder(encoderOfStruct(cfg, typ))
case reflect.Array:
return prefix("[array]").addToEncoder(encoderOfArray(cfg, typ))
case reflect.Slice:
return prefix("[slice]").addToEncoder(encoderOfSlice(cfg, typ))
case reflect.Map:
return prefix("[map]").addToEncoder(encoderOfMap(cfg, typ))
case reflect.Ptr:
return prefix("[optional]").addToEncoder(encoderOfOptional(cfg, typ))
default:
return nil, fmt.Errorf("unsupported type: %v", typ)
}
}
func decoderOfOptional(cfg *frozenConfig, typ reflect.Type) (ValDecoder, error) {
elemType := typ.Elem()
decoder, err := decoderOfType(cfg, elemType)
if err != nil {
return nil, err
}
return &optionalDecoder{elemType, decoder}, nil
}
func encoderOfOptional(cfg *frozenConfig, typ reflect.Type) (ValEncoder, error) {
elemType := typ.Elem()
elemEncoder, err := encoderOfType(cfg, elemType)
if err != nil {
return nil, err
}
encoder := &optionalEncoder{elemEncoder}
if elemType.Kind() == reflect.Map {
encoder = &optionalEncoder{encoder}
}
return encoder, nil
}
func decoderOfMap(cfg *frozenConfig, typ reflect.Type) (ValDecoder, error) {
decoder, err := decoderOfType(cfg, typ.Elem())
if err != nil {
return nil, err
}
mapInterface := reflect.New(typ).Interface()
return &mapDecoder{typ, typ.Key(), typ.Elem(), decoder, extractInterface(mapInterface)}, nil
}
func extractInterface(val interface{}) emptyInterface {
return *((*emptyInterface)(unsafe.Pointer(&val)))
}
func encoderOfMap(cfg *frozenConfig, typ reflect.Type) (ValEncoder, error) {
elemType := typ.Elem()
encoder, err := encoderOfType(cfg, elemType)
if err != nil {
return nil, err
}
mapInterface := reflect.New(typ).Elem().Interface()
if cfg.sortMapKeys {
return &sortKeysMapEncoder{typ, elemType, encoder, *((*emptyInterface)(unsafe.Pointer(&mapInterface)))}, nil
}
return &mapEncoder{typ, elemType, encoder, *((*emptyInterface)(unsafe.Pointer(&mapInterface)))}, nil
}