4_marshallers_test.go

// Package json_test demonstrates custom JSON marshaling in encoding/json/v2 using MarshalFunc
// for type-specific serialization logic without implementing the Marshaler interface.
//
// This file shows:
//   - Using jsonv2.MarshalFunc for custom type serialization
//   - Custom marshaling example: Converting musical notation to Unicode symbols (♯, ♭, °)
//   - Type-safe custom marshaling without modifying the original type
package json_test

import (
	jsonv2 "encoding/json/v2"
	"fmt"
	"strings"
	"testing"
)

type Note string

// noteMarshalFunc is a custom JSON marshaler for Note types that converts musical note notation
// to Unicode symbols (# to ♯, B to ♭, etc.) and normalizes chord notation (MAJ to Maj, M to m, DIM to °).
// Special handling for notes starting with "B" to distinguish flat(♭) notes from B notes.
var noteMarshalFunc = jsonv2.MarshalFunc(func(n Note) ([]byte, error) {
	replacer := strings.NewReplacer(
		"X", "B",
		"#", "♯",
		"B", "♭",
		"MAJ", "Maj",
		"M", "m",
		"DIM", "°",
	)

	str := strings.ToUpper(string(n))
	if strings.HasPrefix(str, "B") {
		str = strings.Replace(str, "B", "X", 1)
	}

	str = replacer.Replace(str)

	return fmt.Append(nil, `"`+str+`"`), nil
})

// TestMarshalCustomType demonstrates using jsonv2.MarshalFunc to provide custom marshaling logic
// for the Note type, converting musical notation (Gbmaj7) to Unicode symbols (G♭Maj7).
func TestMarshalCustomType(t *testing.T) {
	n := Note("Gbmaj7")

	data := struct {
		Name Note
	}{Name: n}

	b, _ := jsonv2.Marshal(data, jsonv2.WithMarshalers(noteMarshalFunc))

	expected := `{"Name":"G♭Maj7"}`

	if string(b) != expected {
		t.Errorf("expected %q, got %q", expected, string(b))
	}
}