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e36aeda | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 | // Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build goexperiment.jsonv2
package json_test
import (
"fmt"
"log"
"reflect"
"encoding/json/jsontext"
"encoding/json/v2"
)
// OrderedObject is an ordered sequence of name/value members in a JSON object.
//
// RFC 8259 defines an object as an "unordered collection".
// JSON implementations need not make "ordering of object members visible"
// to applications nor will they agree on the semantic meaning of an object if
// "the names within an object are not unique". For maximum compatibility,
// applications should avoid relying on ordering or duplicity of object names.
type OrderedObject[V any] []ObjectMember[V]
// ObjectMember is a JSON object member.
type ObjectMember[V any] struct {
Name string
Value V
}
// MarshalJSONTo encodes obj as a JSON object into enc.
func (obj *OrderedObject[V]) MarshalJSONTo(enc *jsontext.Encoder) error {
if err := enc.WriteToken(jsontext.BeginObject); err != nil {
return err
}
for i := range *obj {
member := &(*obj)[i]
if err := json.MarshalEncode(enc, &member.Name); err != nil {
return err
}
if err := json.MarshalEncode(enc, &member.Value); err != nil {
return err
}
}
if err := enc.WriteToken(jsontext.EndObject); err != nil {
return err
}
return nil
}
// UnmarshalJSONFrom decodes a JSON object from dec into obj.
func (obj *OrderedObject[V]) UnmarshalJSONFrom(dec *jsontext.Decoder) error {
if k := dec.PeekKind(); k != '{' {
// The [json] package automatically populates relevant fields
// in a [json.SemanticError] to provide additional context.
return &json.SemanticError{JSONKind: k}
}
if _, err := dec.ReadToken(); err != nil {
return err
}
for dec.PeekKind() != '}' {
*obj = append(*obj, ObjectMember[V]{})
member := &(*obj)[len(*obj)-1]
if err := json.UnmarshalDecode(dec, &member.Name); err != nil {
return err
}
if err := json.UnmarshalDecode(dec, &member.Value); err != nil {
return err
}
}
if _, err := dec.ReadToken(); err != nil {
return err
}
return nil
}
// The exact order of JSON object can be preserved through the use of a
// specialized type that implements [MarshalerTo] and [UnmarshalerFrom].
func Example_orderedObject() {
// Round-trip marshal and unmarshal an ordered object.
// We expect the order and duplicity of JSON object members to be preserved.
// Specify jsontext.AllowDuplicateNames since this object contains "fizz" twice.
want := OrderedObject[string]{
{"fizz", "buzz"},
{"hello", "world"},
{"fizz", "wuzz"},
}
b, err := json.Marshal(&want, jsontext.AllowDuplicateNames(true))
if err != nil {
log.Fatal(err)
}
var got OrderedObject[string]
err = json.Unmarshal(b, &got, jsontext.AllowDuplicateNames(true))
if err != nil {
log.Fatal(err)
}
// Sanity check.
if !reflect.DeepEqual(got, want) {
log.Fatalf("roundtrip mismatch: got %v, want %v", got, want)
}
// Print the serialized JSON object.
(*jsontext.Value)(&b).Indent() // indent for readability
fmt.Println(string(b))
// Output:
// {
// "fizz": "buzz",
// "hello": "world",
// "fizz": "wuzz"
// }
}
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