Golang Value.Cap方法代码示例

func (d *Decoder) decodeBinary(b []byte, v reflect.Value) error {
	if v.Kind() == reflect.Interface {
		buf := make([]byte, len(b))
		copy(buf, b)
		v.Set(reflect.ValueOf(buf))
		return nil
	}

	switch v.Interface().(type) {
	case []byte:
		if v.IsNil() || v.Cap() < len(b) {
			v.Set(reflect.MakeSlice(byteSliceType, len(b), len(b)))
		} else if v.Len() != len(b) {
			v.SetLen(len(b))
		}
		copy(v.Interface().([]byte), b)
	default:
		if v.Kind() == reflect.Array && v.Type().Elem().Kind() == reflect.Uint8 {
			reflect.Copy(v, reflect.ValueOf(b))
			break
		}
		return &UnmarshalTypeError{Value: "binary", Type: v.Type()}
	}

	return nil
}

func (f *decFnInfo) kSlice(rv reflect.Value) {
	// A slice can be set from a map or array in stream.
	currEncodedType := f.dd.currentEncodedType()

	switch currEncodedType {
	case valueTypeBytes, valueTypeString:
		if f.ti.rtid == uint8SliceTypId || f.ti.rt.Elem().Kind() == reflect.Uint8 {
			if bs2, changed2 := f.dd.decodeBytes(rv.Bytes()); changed2 {
				rv.SetBytes(bs2)
			}
			return
		}
	}

	if shortCircuitReflectToFastPath && rv.CanAddr() {
		switch f.ti.rtid {
		case intfSliceTypId:
			f.d.decSliceIntf(rv.Addr().Interface().(*[]interface{}), currEncodedType, f.array)
			return
		case uint64SliceTypId:
			f.d.decSliceUint64(rv.Addr().Interface().(*[]uint64), currEncodedType, f.array)
			return
		case int64SliceTypId:
			f.d.decSliceInt64(rv.Addr().Interface().(*[]int64), currEncodedType, f.array)
			return
		case strSliceTypId:
			f.d.decSliceStr(rv.Addr().Interface().(*[]string), currEncodedType, f.array)
			return
		}
	}

	containerLen, containerLenS := decContLens(f.dd, currEncodedType)

	// an array can never return a nil slice. so no need to check f.array here.

	if rv.IsNil() {
		rv.Set(reflect.MakeSlice(f.ti.rt, containerLenS, containerLenS))
	}

	if containerLen == 0 {
		return
	}

	if rvcap, rvlen := rv.Len(), rv.Cap(); containerLenS > rvcap {
		if f.array { // !rv.CanSet()
			decErr(msgDecCannotExpandArr, rvcap, containerLenS)
		}
		rvn := reflect.MakeSlice(f.ti.rt, containerLenS, containerLenS)
		if rvlen > 0 {
			reflect.Copy(rvn, rv)
		}
		rv.Set(rvn)
	} else if containerLenS > rvlen {
		rv.SetLen(containerLenS)
	}

	for j := 0; j < containerLenS; j++ {
		f.d.decodeValue(rv.Index(j))
	}
}

func (p *Decoder) unmarshalArray(pval *plistValue, val reflect.Value) {
	subvalues := pval.value.([]*plistValue)

	var n int
	if val.Kind() == reflect.Slice {
		// Slice of element values.
		// Grow slice.
		cnt := len(subvalues) + val.Len()
		if cnt >= val.Cap() {
			ncap := 2 * cnt
			if ncap < 4 {
				ncap = 4
			}
			new := reflect.MakeSlice(val.Type(), val.Len(), ncap)
			reflect.Copy(new, val)
			val.Set(new)
		}
		n = val.Len()
		val.SetLen(cnt)
	} else if val.Kind() == reflect.Array {
		if len(subvalues) > val.Cap() {
			panic(fmt.Errorf("plist: attempted to unmarshal %d values into an array of size %d", len(subvalues), val.Cap()))
		}
	} else {
		panic(&incompatibleDecodeTypeError{val.Type(), pval.kind})
	}

	// Recur to read element into slice.
	for _, sval := range subvalues {
		p.unmarshal(sval, val.Index(n))
		n++
	}
	return
}

// grow grows the slice s so that it can hold extra more values, allocating
// more capacity if needed. It also returns the old and new slice lengths.
func grow(s reflect.Value, extra int) (reflect.Value, int, int) {
	i0 := s.Len()
	i1 := i0 + extra
	if i1 < i0 {
		panic("reflect.Append: slice overflow")
	}
	m := s.Cap()
	if i1 <= m {
		return s.Slice(0, i1), i0, i1
	}
	if m == 0 {
		m = extra
	} else {
		for m < i1 {
			if i0 < 1024 {
				m += m
			} else {
				m += m / 4
			}
		}
	}
	t := reflect.MakeSlice(s.Type(), i1, m)
	reflect.Copy(t, s)
	return t, i0, i1
}

func (f *Field) Unpack(buf []byte, val reflect.Value, length int, options *Options) error {
	typ := f.Type.Resolve(options)
	if typ == Pad || f.kind == reflect.String {
		if typ == Pad {
			return nil
		} else {
			val.SetString(string(buf))
			return nil
		}
	} else if f.Slice {
		if val.Cap() < length {
			val.Set(reflect.MakeSlice(val.Type(), length, length))
		} else if val.Len() < length {
			val.Set(val.Slice(0, length))
		}
		// special case byte slices for performance
		if !f.Array && typ == Uint8 && f.defType == Uint8 {
			copy(val.Bytes(), buf[:length])
			return nil
		}
		pos := 0
		size := typ.Size()
		for i := 0; i < length; i++ {
			if err := f.unpackVal(buf[pos:pos+size], val.Index(i), 1, options); err != nil {
				return err
			}
			pos += size
		}
		return nil
	} else {
		return f.unpackVal(buf, val, length, options)
	}
}

func (d *Decoder) decodeList(avList []*dynamodb.AttributeValue, v reflect.Value) error {
	switch v.Kind() {
	case reflect.Slice:
		// Make room for the slice elements if needed
		if v.IsNil() || v.Cap() < len(avList) {
			// What about if ignoring nil/empty values?
			v.Set(reflect.MakeSlice(v.Type(), 0, len(avList)))
		}
	case reflect.Array:
		// Limited to capacity of existing array.
	case reflect.Interface:
		s := make([]interface{}, len(avList))
		for i, av := range avList {
			if err := d.decode(av, reflect.ValueOf(&s[i]).Elem(), tag{}); err != nil {
				return err
			}
		}
		v.Set(reflect.ValueOf(s))
		return nil
	default:
		return &UnmarshalTypeError{Value: "list", Type: v.Type()}
	}

	// If v is not a slice, array
	for i := 0; i < v.Cap() && i < len(avList); i++ {
		v.SetLen(i + 1)
		if err := d.decode(avList[i], v.Index(i), tag{}); err != nil {
			return err
		}
	}

	return nil
}

func (d *Decoder) decodeStringSet(ss []*string, v reflect.Value) error {
	switch v.Kind() {
	case reflect.Slice:
		// Make room for the slice elements if needed
		if v.IsNil() || v.Cap() < len(ss) {
			v.Set(reflect.MakeSlice(v.Type(), 0, len(ss)))
		}
	case reflect.Array:
		// Limited to capacity of existing array.
	case reflect.Interface:
		set := make([]string, len(ss))
		for i, s := range ss {
			if err := d.decodeString(s, reflect.ValueOf(&set[i]).Elem(), tag{}); err != nil {
				return err
			}
		}
		v.Set(reflect.ValueOf(set))
		return nil
	default:
		return &UnmarshalTypeError{Value: "string set", Type: v.Type()}
	}

	for i := 0; i < v.Cap() && i < len(ss); i++ {
		v.SetLen(i + 1)
		u, elem := indirect(v.Index(i), false)
		if u != nil {
			return u.UnmarshalDynamoDBAttributeValue(&dynamodb.AttributeValue{SS: ss})
		}
		if err := d.decodeString(ss[i], elem, tag{}); err != nil {
			return err
		}
	}

	return nil
}

func setSliceField(value reflect.Value, str string, ctx *context) error {
	if ctx.defaultVal != "" {
		return ErrDefaultUnsupportedOnSlice
	}

	elType := value.Type().Elem()
	tnz := newSliceTokenizer(str)

	slice := reflect.MakeSlice(value.Type(), value.Len(), value.Cap())

	for tnz.scan() {
		token := tnz.text()

		el := reflect.New(elType).Elem()

		if err := parseValue(el, token, ctx); err != nil {
			return err
		}

		slice = reflect.Append(slice, el)
	}

	value.Set(slice)

	return tnz.Err()
}

// Validate checks whether the given value is writeable to this schema.
func (*NullSchema) Validate(v reflect.Value) bool {
	// Check if the value is something that can be null
	switch v.Kind() {
	case reflect.Interface:
		return v.IsNil()
	case reflect.Array:
		return v.Cap() == 0
	case reflect.Slice:
		return v.IsNil() || v.Cap() == 0
	case reflect.Map:
		return len(v.MapKeys()) == 0
	case reflect.String:
		return len(v.String()) == 0
	case reflect.Float32:
		// Should NaN floats be treated as null?
		return math.IsNaN(v.Float())
	case reflect.Float64:
		// Should NaN floats be treated as null?
		return math.IsNaN(v.Float())
	case reflect.Ptr:
		return v.IsNil()
	case reflect.Invalid:
		return true
	}

	// Nothing else in particular, so this should not validate?
	return false
}

func ensureLen(d reflect.Value, n int) {
	if n > d.Cap() {
		d.Set(reflect.MakeSlice(d.Type(), n, n))
	} else {
		d.SetLen(n)
	}
}

func deStructSlice(dataValue reflect.Value) (interface{}, interface{}, map[string]interface{}) {
	if dataValue.Kind() == reflect.Uint8 {
		newDataValue := reflect.MakeSlice(dataValue.Type(), dataValue.Len(), dataValue.Cap())
		newDataValue = reflect.AppendSlice(newDataValue, dataValue)
		return newDataValue.Interface(), newDataValue.Interface(), nil
	}

	//TODO if the type inside the slice is not a struct, recreate the slice with the same definition
	newData := make([]interface{}, dataValue.Len())
	flatData := make(map[string]interface{})
	for i := 0; i < dataValue.Len(); i++ {
		subDataValue := dataValue.Index(i)
		key := strconv.Itoa(i)

		fieldCopy, fieldScalar, fieldMap := deStructValue(subDataValue)
		newData[i] = fieldCopy

		if fieldScalar != nil {
			flatData[key] = fieldScalar
		}
		for fieldMapKey, fieldMapValue := range fieldMap {
			flatData[key+"."+fieldMapKey] = fieldMapValue
		}
	}

	return newData, nil, flatData
}

// rcopy performs a recursive copy of values from the source to destination.
//
// root is used to skip certain aspects of the copy which are not valid
// for the root node of a object.
func rcopy(dst, src reflect.Value, root bool) {
	if !src.IsValid() {
		return
	}

	switch src.Kind() {
	case reflect.Ptr:
		if _, ok := src.Interface().(io.Reader); ok {
			if dst.Kind() == reflect.Ptr && dst.Elem().CanSet() {
				dst.Elem().Set(src)
			} else if dst.CanSet() {
				dst.Set(src)
			}
		} else {
			e := src.Type().Elem()
			if dst.CanSet() && !src.IsNil() {
				dst.Set(reflect.New(e))
			}
			if src.Elem().IsValid() {
				// Keep the current root state since the depth hasn't changed
				rcopy(dst.Elem(), src.Elem(), root)
			}
		}
	case reflect.Struct:
		if !root {
			dst.Set(reflect.New(src.Type()).Elem())
		}

		t := dst.Type()
		for i := 0; i < t.NumField(); i++ {
			name := t.Field(i).Name
			srcval := src.FieldByName(name)
			if srcval.IsValid() {
				rcopy(dst.FieldByName(name), srcval, false)
			}
		}
	case reflect.Slice:
		s := reflect.MakeSlice(src.Type(), src.Len(), src.Cap())
		dst.Set(s)
		for i := 0; i < src.Len(); i++ {
			rcopy(dst.Index(i), src.Index(i), false)
		}
	case reflect.Map:
		s := reflect.MakeMap(src.Type())
		dst.Set(s)
		for _, k := range src.MapKeys() {
			v := src.MapIndex(k)
			v2 := reflect.New(v.Type()).Elem()
			rcopy(v2, v, false)
			dst.SetMapIndex(k, v2)
		}
	default:
		// Assign the value if possible. If its not assignable, the value would
		// need to be converted and the impact of that may be unexpected, or is
		// not compatible with the dst type.
		if src.Type().AssignableTo(dst.Type()) {
			dst.Set(src)
		}
	}
}

// NewChannelDescriptor creates a ChannelDescriptor for the channel in the
// parameter
func NewChannelDescriptor(val reflect.Value) *ChannelDescriptor {
	t := val.Type()
	return &ChannelDescriptor{
		Dir:      t.ChanDir(),
		TypeName: types.NameOf(t.Elem()),
		Size:     val.Cap(),
	}
}

func (d *sliceDecoder) decode(dv, sv reflect.Value) {
	if dv.Kind() == reflect.Slice {
		dv.Set(reflect.MakeSlice(dv.Type(), dv.Len(), dv.Cap()))
	}

	if !sv.IsNil() {
		d.arrayDec(dv, sv)
	}
}

//FIXME: fix when v is invalid
// type(1) | name length(1) | item size(4) | raw name bytes | 0x00
// | element number(4) | element1 | ... | elementN
func (d *decodeState) array(v reflect.Value) {
	d.off += 1 // type

	klen := int(Int8(d.data[d.off:]))
	d.off += 1 // name length

	// vlen := int(Int32(d.data[d.off:]))
	d.off += 4 //  content length

	//var key string
	if klen > 0 {
		key := d.data[d.off : d.off+klen-1]
		d.off += klen
		v = fieldByTag(v, key)
		u, pv := d.indirect(v, false)
		if u != nil {
			d.off -= 1 + 1 + 4 + klen
			if err := u.UnmarshalMCPACK(d.next()); err != nil {
				d.error(err)
			}
			return
		}
		v = pv
	}

	n := int(Int32(d.data[d.off:]))
	d.off += 4 // member number

	if v.Kind() == reflect.Slice {
		if n > v.Cap() {
			newv := reflect.MakeSlice(v.Type(), n, n)
			v.Set(newv)
		}
		v.SetLen(n)
	}

	for i := 0; i < n; i++ {
		if i < v.Len() {
			d.value(v.Index(i))
		} else {
			d.value(reflect.Value{})
		}
	}

	if n < v.Len() {
		if v.Kind() == reflect.Array {
			z := reflect.Zero(v.Type().Elem())
			for i := 0; i < v.Len(); i++ {
				v.Index(i).Set(z)
			}
		}
	}

	if n == 0 && v.Kind() == reflect.Slice {
		v.Set(reflect.MakeSlice(v.Type(), 0, 0))
	}
}