Golang reflect.MakeZero函数代码示例

// decodeInterface receives the name of a concrete type followed by its value.
// If the name is empty, the value is nil and no value is sent.
func (dec *Decoder) decodeInterface(ityp *reflect.InterfaceType, state *decodeState, p uintptr, indir int) {
	// Create an interface reflect.Value.  We need one even for the nil case.
	ivalue := reflect.MakeZero(ityp).(*reflect.InterfaceValue)
	// Read the name of the concrete type.
	b := make([]byte, state.decodeUint())
	state.b.Read(b)
	name := string(b)
	if name == "" {
		// Copy the representation of the nil interface value to the target.
		// This is horribly unsafe and special.
		*(*[2]uintptr)(unsafe.Pointer(p)) = ivalue.Get()
		return
	}
	// The concrete type must be registered.
	typ, ok := nameToConcreteType[name]
	if !ok {
		errorf("gob: name not registered for interface: %q", name)
	}
	// Read the concrete value.
	value := reflect.MakeZero(typ)
	dec.decodeValueFromBuffer(value, false, true)
	if dec.err != nil {
		error(dec.err)
	}
	// Allocate the destination interface value.
	if indir > 0 {
		p = allocate(ityp, p, 1) // All but the last level has been allocated by dec.Indirect
	}
	// Assign the concrete value to the interface.
	// Tread carefully; it might not satisfy the interface.
	setInterfaceValue(ivalue, value)
	// Copy the representation of the interface value to the target.
	// This is horribly unsafe and special.
	*(*[2]uintptr)(unsafe.Pointer(p)) = ivalue.Get()
}

func (jm *jsonDemarshaler) Demarshal() (id Id, ctrlMsg interface{}, appMsg reflect.Value, err os.Error) {
	seedId := jm.proxy.router.seedId
	id, _ = seedId.Clone()
	if err = jm.Decode(id); err != nil {
		return
	}
	if id.Scope() == NumScope && id.Member() == NumMembership {
		return
	}
	switch id.SysIdIndex() {
	case ConnId, DisconnId, ErrorId:
		idc, _ := seedId.Clone()
		ctrlMsg = &ConnInfoMsg{Id: idc}
		err = jm.demarshalCtrlMsg(ctrlMsg)
	case ReadyId:
		idc, _ := seedId.Clone()
		ctrlMsg = &ConnReadyMsg{[]*ChanReadyInfo{&ChanReadyInfo{Id: idc}}}
		err = jm.demarshalCtrlMsg(ctrlMsg)
	case PubId, UnPubId, SubId, UnSubId:
		idc, _ := seedId.Clone()
		ctrlMsg = &IdChanInfoMsg{[]*IdChanInfo{&IdChanInfo{idc, nil, nil}}}
		err = jm.demarshalCtrlMsg(ctrlMsg)
	default: //appMsg
		chanType := jm.proxy.getExportRecvChanType(id)
		if chanType == nil {
			err = os.ErrorString(fmt.Sprintf("failed to find chanType for id %v", id))
			return
		}
		et := chanType.Elem()
		appMsg = reflect.MakeZero(et)
		var ptrT *reflect.PtrValue
		switch et := et.(type) {
		case *reflect.BoolType:
			ptrT = jm.ptrBool
			ptrT.PointTo(appMsg)
		case *reflect.IntType:
			ptrT = jm.ptrInt
			ptrT.PointTo(appMsg)
		case *reflect.FloatType:
			ptrT = jm.ptrFloat
			ptrT.PointTo(appMsg)
		case *reflect.StringType:
			ptrT = jm.ptrString
			ptrT.PointTo(appMsg)
		case *reflect.PtrType:
			sto := reflect.MakeZero(et.Elem())
			ptrT = appMsg.(*reflect.PtrValue)
			ptrT.PointTo(sto)
		default:
			err = os.ErrorString(fmt.Sprintf("invalid chanType for id %v", id))
			return
		}
		err = jm.Decode(ptrT.Interface())
	}
	return
}

func TestUnmarshal(t *testing.T) {
	for i, test := range unmarshalTestData {
		pv := reflect.MakeZero(reflect.NewValue(test.out).Type())
		zv := reflect.MakeZero(pv.Type().(*reflect.PtrType).Elem())
		pv.(*reflect.PtrValue).PointTo(zv)
		val := pv.Interface()
		err := Unmarshal(val, test.in)
		if err != nil {
			t.Errorf("Unmarshal failed at index %d %v", i, err)
		}
		if !reflect.DeepEqual(val, test.out) {
			t.Errorf("#%d:\nhave %#v\nwant %#v", i, val, test.out)
		}
	}
}

// subst returns a copy of pattern with values from m substituted in place
// of wildcards and pos used as the position of tokens from the pattern.
// if m == nil, subst returns a copy of pattern and doesn't change the line
// number information.
func subst(m map[string]reflect.Value, pattern reflect.Value, pos reflect.Value) reflect.Value {
	if pattern == nil {
		return nil
	}

	// Wildcard gets replaced with map value.
	if m != nil && pattern.Type() == identType {
		name := pattern.Interface().(*ast.Ident).Name()
		if isWildcard(name) {
			if old, ok := m[name]; ok {
				return subst(nil, old, nil)
			}
		}
	}

	if pos != nil && pattern.Type() == positionType {
		return pos
	}

	// Otherwise copy.
	switch p := pattern.(type) {
	case *reflect.SliceValue:
		v := reflect.MakeSlice(p.Type().(*reflect.SliceType), p.Len(), p.Len())
		for i := 0; i < p.Len(); i++ {
			v.Elem(i).SetValue(subst(m, p.Elem(i), pos))
		}
		return v

	case *reflect.StructValue:
		v := reflect.MakeZero(p.Type()).(*reflect.StructValue)
		for i := 0; i < p.NumField(); i++ {
			v.Field(i).SetValue(subst(m, p.Field(i), pos))
		}
		return v

	case *reflect.PtrValue:
		v := reflect.MakeZero(p.Type()).(*reflect.PtrValue)
		v.PointTo(subst(m, p.Elem(), pos))
		return v

	case *reflect.InterfaceValue:
		v := reflect.MakeZero(p.Type()).(*reflect.InterfaceValue)
		v.SetValue(subst(m, p.Elem(), pos))
		return v
	}

	return pattern
}

func writeToContainer(data [][]byte, val reflect.Value) os.Error {
	switch v := val.(type) {
	case *reflect.PtrValue:
		return writeToContainer(data, reflect.Indirect(v))
	case *reflect.InterfaceValue:
		return writeToContainer(data, v.Elem())
	case *reflect.MapValue:
		if _, ok := v.Type().(*reflect.MapType).Key().(*reflect.StringType); !ok {
			return os.NewError("Invalid map type")
		}
		elemtype := v.Type().(*reflect.MapType).Elem()
		for i := 0; i < len(data)/2; i++ {
			mk := reflect.NewValue(string(data[i*2]))
			mv := reflect.MakeZero(elemtype)
			writeTo(data[i*2+1], mv)
			v.SetElem(mk, mv)
		}
	case *reflect.StructValue:
		for i := 0; i < len(data)/2; i++ {
			name := string(data[i*2])
			field := v.FieldByName(name)
			if field == nil {
				continue
			}
			writeTo(data[i*2+1], field)
		}
	default:
		return os.NewError("Invalid container type")
	}
	return nil
}

func TestUnmarshal(t *testing.T) {
	var scan scanner
	for i, tt := range unmarshalTests {
		in := []byte(tt.in)
		if err := checkValid(in, &scan); err != nil {
			t.Errorf("#%d: checkValid: %v", i, err)
			continue
		}
		// v = new(right-type)
		v := reflect.NewValue(tt.ptr).(*reflect.PtrValue)
		v.PointTo(reflect.MakeZero(v.Type().(*reflect.PtrType).Elem()))
		if err := Unmarshal([]byte(in), v.Interface()); err != nil {
			t.Errorf("#%d: %v", i, err)
			continue
		}
		if !reflect.DeepEqual(v.Elem().Interface(), tt.out) {
			t.Errorf("#%d: mismatch\nhave: %#+v\nwant: %#+v", i, v.Elem().Interface(), tt.out)
			data, _ := Marshal(v.Elem().Interface())
			println(string(data))
			data, _ = Marshal(tt.out)
			println(string(data))
			return
			continue
		}
	}
}

func (b *structBuilder) Key(k string) Builder {
	if b == nil {
		return nobuilder
	}
	switch v := reflect.Indirect(b.val).(type) {
	case *reflect.StructValue:
		t := v.Type().(*reflect.StructType)
		// Case-insensitive field lookup.
		k = strings.ToLower(k)
		for i := 0; i < t.NumField(); i++ {
			if strings.ToLower(t.Field(i).Name) == k {
				return &structBuilder{val: v.Field(i)}
			}
		}
	case *reflect.MapValue:
		t := v.Type().(*reflect.MapType)
		if t.Key() != reflect.Typeof(k) {
			break
		}
		key := reflect.NewValue(k)
		elem := v.Elem(key)
		if elem == nil {
			v.SetElem(key, reflect.MakeZero(t.Elem()))
			elem = v.Elem(key)
		}
		return &structBuilder{val: elem, map_: v, key: key}
	}
	return nobuilder
}

// ImportNValues imports a channel of the given type and specified direction
// and then receives or transmits up to n values on that channel.  A value of
// n==0 implies an unbounded number of values.  The channel to be bound to
// the remote site's channel is provided in the call and may be of arbitrary
// channel type.
// Despite the literal signature, the effective signature is
//	ImportNValues(name string, chT chan T, dir Dir, pT T)
// where T must be a struct, pointer to struct, etc.  pT may be more indirect
// than the value type of the channel (e.g.  chan T, pT *T) but it must be a
// pointer.
// Example usage:
//	imp, err := NewImporter("tcp", "netchanserver.mydomain.com:1234")
//	if err != nil { log.Exit(err) }
//	ch := make(chan myType)
//	err := imp.ImportNValues("name", ch, Recv, new(myType), 1)
//	if err != nil { log.Exit(err) }
//	fmt.Printf("%+v\n", <-ch)
// (TODO: Can we eliminate the need for pT?)
func (imp *Importer) ImportNValues(name string, chT interface{}, dir Dir, pT interface{}, n int) os.Error {
	ch, err := checkChan(chT, dir)
	if err != nil {
		return err
	}
	// Make sure pT is a pointer (to a pointer...) to a struct.
	rt := reflect.Typeof(pT)
	if _, ok := rt.(*reflect.PtrType); !ok {
		return os.ErrorString("not a pointer:" + rt.String())
	}
	if _, ok := reflect.Indirect(reflect.NewValue(pT)).(*reflect.StructValue); !ok {
		return os.ErrorString("not a pointer to a struct:" + rt.String())
	}
	imp.chanLock.Lock()
	defer imp.chanLock.Unlock()
	_, present := imp.chans[name]
	if present {
		return os.ErrorString("channel name already being imported:" + name)
	}
	ptr := reflect.MakeZero(reflect.Typeof(pT)).(*reflect.PtrValue)
	imp.chans[name] = &importChan{ch, dir, ptr, n}
	// Tell the other side about this channel.
	req := new(request)
	req.name = name
	req.dir = dir
	req.count = n
	if err := imp.encode(req, nil); err != nil {
		log.Stderr("importer request encode:", err)
		return err
	}
	return nil
}

func (c *Conn) GetAll(rowsSlicePtr interface{}, condition string, args ...interface{}) os.Error {
	sliceValue, ok := reflect.Indirect(reflect.NewValue(rowsSlicePtr)).(*reflect.SliceValue)
	if !ok {
		return os.NewError("needs a pointer to a slice")
	}

	sliceElementType := sliceValue.Type().(*reflect.SliceType).Elem()

	condition = strings.TrimSpace(condition)
	if len(condition) > 0 {
		condition = fmt.Sprintf("where %v", condition)
	}

	resultsSlice, err := c.getResultsForQuery(getTableName(rowsSlicePtr), condition, args)
	if err != nil {
		return err
	}

	for _, results := range resultsSlice {
		newValue := reflect.MakeZero(sliceElementType)
		scanMapIntoStruct(newValue.Addr().Interface(), results)
		sliceValue.SetValue(reflect.Append(sliceValue, newValue))
	}

	return nil
}

// Handle the data from a single imported data stream, which will
// have the form
//	(response, data)*
// The response identifies by name which channel is receiving data.
// TODO: allow an importer to send.
func (imp *Importer) run() {
	// Loop on responses; requests are sent by ImportNValues()
	resp := new(response)
	for {
		if err := imp.decode(resp); err != nil {
			log.Stderr("importer response decode:", err)
			break
		}
		if resp.error != "" {
			log.Stderr("importer response error:", resp.error)
			// TODO: tear down connection
			break
		}
		imp.chanLock.Lock()
		ich, ok := imp.chans[resp.name]
		imp.chanLock.Unlock()
		if !ok {
			log.Stderr("unknown name in request:", resp.name)
			break
		}
		if ich.dir != Recv {
			log.Stderr("TODO: import send unimplemented")
			break
		}
		// Create a new value for each received item.
		val := reflect.MakeZero(ich.ptr.Type().(*reflect.PtrType).Elem())
		ich.ptr.PointTo(val)
		if err := imp.decode(ich.ptr.Interface()); err != nil {
			log.Stderr("importer value decode:", err)
			return
		}
		ich.ch.Send(val)
	}
}

func TestDecodeStruct(t *testing.T) {
	for i, bt := range bsonTests {
		if bt.psv == nil {
			continue
		}
		pt := reflect.NewValue(bt.psv).Type().(*reflect.PtrType)
		psv := reflect.MakeZero(pt).(*reflect.PtrValue)
		psv.PointTo(reflect.MakeZero(pt.Elem()))
		err := Decode(bt.data, psv.Interface())
		sv := psv.Elem().Interface()
		if err != nil {
			t.Errorf("%d: error decoding %q: %s", i, bt.data, err)
		} else if !reflect.DeepEqual(sv, bt.sv) {
			t.Errorf("%d: data=%q,\n\texpected %q\n\tactual  %q", i, bt.data, bt.sv, sv)
		}
	}
}

func (dec *Decoder) decodeMap(mtyp *reflect.MapType, state *decodeState, p uintptr, keyOp, elemOp decOp, indir, keyIndir, elemIndir int, ovfl os.ErrorString) {
	if indir > 0 {
		p = allocate(mtyp, p, 1) // All but the last level has been allocated by dec.Indirect
	}
	up := unsafe.Pointer(p)
	if *(*unsafe.Pointer)(up) == nil { // maps are represented as a pointer in the runtime
		// Allocate map.
		*(*unsafe.Pointer)(up) = unsafe.Pointer(reflect.MakeMap(mtyp).Get())
	}
	// Maps cannot be accessed by moving addresses around the way
	// that slices etc. can.  We must recover a full reflection value for
	// the iteration.
	v := reflect.NewValue(unsafe.Unreflect(mtyp, unsafe.Pointer((p)))).(*reflect.MapValue)
	n := int(state.decodeUint())
	for i := 0; i < n; i++ {
		key := decodeIntoValue(state, keyOp, keyIndir, reflect.MakeZero(mtyp.Key()), ovfl)
		elem := decodeIntoValue(state, elemOp, elemIndir, reflect.MakeZero(mtyp.Elem()), ovfl)
		v.SetElem(key, elem)
	}
}

// Receive and deliver locally one item from a client asking for a Send
// The header is passed by value to avoid issues of overwriting.
func (client *expClient) serveSend(hdr header) {
	ech := client.getChan(&hdr, Recv)
	if ech == nil {
		return
	}
	// Create a new value for each received item.
	val := reflect.MakeZero(ech.ch.Type().(*reflect.ChanType).Elem())
	if err := client.decode(val); err != nil {
		expLog("value decode:", err)
		return
	}
	ech.ch.Send(val)
}

func (self *structBuilder) Key(k string) Builder {
	if self == nil {
		return nobuilder
	}
	switch v := reflect.Indirect(self.val).(type) {
	case *reflect.StructValue:
		t := v.Type().(*reflect.StructType)
		// Case-insensitive field lookup.
		k = strings.ToLower(k)
		for i := 0; i < t.NumField(); i++ {
			if strings.ToLower(t.Field(i).Name) == k {
				return &structBuilder{val: v.Field(i)}
			}
		}

	case *reflect.MapValue:
		t := v.Type().(*reflect.MapType)
		if t.Key() != reflect.Typeof(k) {
			break
		}
		key := reflect.NewValue(k)
		elem := v.Elem(key)
		if elem == nil {
			v.SetElem(key, reflect.MakeZero(t.Elem()))
			elem = v.Elem(key)
		}
		return &structBuilder{val: elem, map_: v, key: key}

	case *reflect.SliceValue:
		index, err := strconv.Atoi(k)
		if err != nil {
			return nobuilder
		}
		if index < v.Len() {
			return &structBuilder{val: v.Elem(index)}
		}
		if index < v.Cap() {
			v.SetLen(index + 1)
			return &structBuilder{val: v.Elem(index)}
		}
		newCap := v.Cap() * 2
		if index >= newCap {
			newCap = index*2 + 1
		}
		temp := reflect.MakeSlice(v.Type().(*reflect.SliceType), index+1, newCap)
		reflect.ArrayCopy(temp, v)
		v.Set(temp)
		return &structBuilder{val: v.Elem(index)}
	}
	return nobuilder
}

func checkUnmarshal(expected string, data any) (err os.Error) {
	if err = checkMarshal(expected, data); err != nil {
		return
	}
	dataValue := reflect.NewValue(data)
	newOne := reflect.MakeZero(dataValue.Type())
	buf := bytes.NewBufferString(expected)
	if err = UnmarshalValue(buf, newOne); err != nil {
		return
	}
	if err = checkFuzzyEqualValue(dataValue, newOne); err != nil {
		return
	}
	return
}