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https://github.com/protocolbuffers/protobuf-go.git
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d4f0800c42
We occasionally need to work with immutable, empty lists, maps, and
messages. Notably, Message.Get on an empty repeated field will return a
"frozen" empty value.
Move handling of these immutable, zero-length composites into Converter,
to unify the behavior of regular and extension fields.
Add a Zero method to Converter, MessageType, and ExtensionType, to
provide a consistent way to get an empty, frozen value of a composite
type. Adding this method to the public {Message,Extension}Type
interfaces does increase our API surface, but lets us (for example)
cleanly represent an empty map as a nil map rather than a non-nil
one wrapped in a frozenMap type.
Drop the frozen{List,Map,Message} types as no longer necessary.
(These types did have support for creating a read-only view of a
non-empty value, but we are not currently using that feature.)
Change-Id: Ia76f149d591da07b40ce75b7404a7ab8a60cb9d8
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/189339
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
77 lines
1.9 KiB
Go
77 lines
1.9 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 impl
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import (
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"fmt"
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"reflect"
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pref "google.golang.org/protobuf/reflect/protoreflect"
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)
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type listConverter struct {
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goType reflect.Type
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c Converter
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}
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func newListConverter(t reflect.Type, fd pref.FieldDescriptor) Converter {
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if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Slice {
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panic(fmt.Sprintf("invalid Go type %v for field %v", t, fd.FullName()))
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}
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return &listConverter{t, newSingularConverter(t.Elem().Elem(), fd)}
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}
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func (c *listConverter) PBValueOf(v reflect.Value) pref.Value {
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if v.Type() != c.goType {
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panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
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}
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return pref.ValueOf(&listReflect{v, c.c})
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}
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func (c *listConverter) GoValueOf(v pref.Value) reflect.Value {
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return v.List().(*listReflect).v
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}
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func (c *listConverter) New() pref.Value {
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return c.PBValueOf(reflect.New(c.goType.Elem()))
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}
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func (c *listConverter) Zero() pref.Value {
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return c.PBValueOf(reflect.Zero(c.goType))
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}
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type listReflect struct {
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v reflect.Value // *[]T
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conv Converter
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}
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func (ls *listReflect) Len() int {
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if ls.v.IsNil() {
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return 0
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}
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return ls.v.Elem().Len()
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}
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func (ls *listReflect) Get(i int) pref.Value {
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return ls.conv.PBValueOf(ls.v.Elem().Index(i))
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}
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func (ls *listReflect) Set(i int, v pref.Value) {
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ls.v.Elem().Index(i).Set(ls.conv.GoValueOf(v))
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}
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func (ls *listReflect) Append(v pref.Value) {
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ls.v.Elem().Set(reflect.Append(ls.v.Elem(), ls.conv.GoValueOf(v)))
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}
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func (ls *listReflect) Truncate(i int) {
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ls.v.Elem().Set(ls.v.Elem().Slice(0, i))
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}
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func (ls *listReflect) NewMessage() pref.Message {
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return ls.NewElement().Message()
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}
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func (ls *listReflect) NewElement() pref.Value {
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return ls.conv.New()
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}
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func (ls *listReflect) ProtoUnwrap() interface{} {
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return ls.v.Interface()
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}
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