mirror of
https://github.com/protocolbuffers/protobuf-go.git
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f6d4a4215f
Clearly specify that Get on an unpopulated field: * returns the default value for scalars * returns a mutable (but empty) List for repeated fields * returns a mutable (but empty) Map for map fields * returns an invalid value for message fields The difference in semantics between List+Maps and Messages is because protobuf semantics provide no distinction between an unpopulated and empty list or map. On the other hand, there is a semantic difference between an unpopulated message and an empty message. Default values for scalars is trivial to implement with FieldDescriptor.Default. A mutable, but empty List and Map is easy to implement for known fields since known fields are generated as a slice or map field in a struct. Since struct fields are addressable, the implementation can just return a reference to the slice or map. Repeated, extension fields are a little more tricky since extension fields are implemented under the hood as a map[FieldNumber]Extension. Rather than allocating an empty list in KnownFields.Get upon first retrieval (which presents a race), delegate the work to ExtensionFieldTypes.Register, which must occur before any Get operation. Register is not a concurrent-safe operation, so that is an excellent time to initilize empty lists. The implementation of extensions will need to be careful that Clear on a repeated field simply truncates it zero instead of deleting the object. For unpopulated messages, we return an invalid value, instead of the prior behavior of returning a typed nil-pointer to the Go type for the message. The approach is problematic because it assumes that 1) all messages are always implemented on a pointer reciever 2) a typed nil-pointer is an appropriate "read-only, but empty" message These assumptions are not true of all message types (e.g., dynamic messages). Change-Id: Ie96e6744c890308d9de738b6cf01d3b19e7e7c6a Reviewed-on: https://go-review.googlesource.com/c/150319 Reviewed-by: Damien Neil <dneil@google.com>
87 lines
2.1 KiB
Go
87 lines
2.1 KiB
Go
// Copyright 2018 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package value
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import (
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"reflect"
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pref "github.com/golang/protobuf/v2/reflect/protoreflect"
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)
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func MapOf(p interface{}, kc, kv Converter) pref.Map {
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// TODO: Validate that p is a *map[K]V?
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rv := reflect.ValueOf(p).Elem()
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return mapReflect{rv, kc, kv}
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}
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type mapReflect struct {
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v reflect.Value // addressable map[K]V
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keyConv Converter
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valConv Converter
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}
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func (ms mapReflect) Len() int {
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return ms.v.Len()
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}
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func (ms mapReflect) Has(k pref.MapKey) bool {
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rk := ms.keyConv.GoValueOf(k.Value())
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rv := ms.v.MapIndex(rk)
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return rv.IsValid()
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}
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func (ms mapReflect) Get(k pref.MapKey) pref.Value {
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rk := ms.keyConv.GoValueOf(k.Value())
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rv := ms.v.MapIndex(rk)
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if !rv.IsValid() {
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return pref.Value{}
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}
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return ms.valConv.PBValueOf(rv)
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}
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func (ms mapReflect) Set(k pref.MapKey, v pref.Value) {
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if ms.v.IsNil() {
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ms.v.Set(reflect.MakeMap(ms.v.Type()))
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}
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rk := ms.keyConv.GoValueOf(k.Value())
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rv := ms.valConv.GoValueOf(v)
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ms.v.SetMapIndex(rk, rv)
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}
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func (ms mapReflect) Clear(k pref.MapKey) {
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rk := ms.keyConv.GoValueOf(k.Value())
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ms.v.SetMapIndex(rk, reflect.Value{})
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}
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func (ms mapReflect) Mutable(k pref.MapKey) pref.Mutable {
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// Mutable is only valid for messages and panics for other kinds.
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if ms.v.IsNil() {
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ms.v.Set(reflect.MakeMap(ms.v.Type()))
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}
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rk := ms.keyConv.GoValueOf(k.Value())
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rv := ms.v.MapIndex(rk)
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if !rv.IsValid() {
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pv := pref.ValueOf(ms.valConv.MessageType.New().ProtoReflect())
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rv = ms.valConv.GoValueOf(pv)
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ms.v.SetMapIndex(rk, rv)
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}
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return ms.valConv.PBValueOf(rv).Message()
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}
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func (ms mapReflect) Range(f func(pref.MapKey, pref.Value) bool) {
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for _, k := range ms.v.MapKeys() {
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if v := ms.v.MapIndex(k); v.IsValid() {
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pk := ms.keyConv.PBValueOf(k).MapKey()
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pv := ms.valConv.PBValueOf(v)
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if !f(pk, pv) {
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return
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}
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}
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}
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}
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func (ms mapReflect) Unwrap() interface{} {
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return ms.v.Addr().Interface()
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}
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func (ms mapReflect) ProtoMutable() {}
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var (
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_ pref.Map = mapReflect{}
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_ Unwrapper = mapReflect{}
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)
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