golang: implementasi fungsi Marshal khusus untuk map & bukan untuk struct . playground: https://play.golang.org/p/nnyHUcCdyaA

README.MD

fungsi Marshal di package encoding/json bisa di pakai baik untuk data type struct maupun data type map sehingga implementasinya harus pakai reflect: https://golang.org/src/encoding/json/encode.go?s=6456:6499#L298 . saya buat fungsi Marshal khusus untuk data type map saja & tidak untuk data type struct sehingga implementasinya bisa tanpa reflect sehingga performa bisa lebih baik

untuk cek kebenaran hasil, bisa pakai JSON.parse di konsol browser:

jsonmap.go

package main

import (
	"bytes"
	"strconv"
)

func fKV(rslt *bytes.Buffer, v KV) {
	i := len(v)
	rslt.WriteByte('{')
	for _k, _v := range v {
		rslt.WriteByte('"')
		rslt.WriteString(_k)
		rslt.WriteString(`":`)
		Marshal(rslt, _v)
		i--
		if i == 0 {
			rslt.WriteByte('}')
			return
		}
		rslt.WriteByte(',')
	}
}
func fSlc(rslt *bytes.Buffer, v Slc) {
	last := len(v) - 1
	rslt.WriteByte('[')
	for _, _v := range v[:last] {
		Marshal(rslt, _v)
		rslt.WriteByte(',')
	}
	Marshal(rslt, v[last])
	rslt.WriteByte(']')
}
func Marshal(rslt *bytes.Buffer, v interface{}) {
	switch v.(type) {
	case string:
		rslt.WriteByte('"')
		rslt.WriteString(v.(string))
		rslt.WriteByte('"')
	case int:
		rslt.WriteString(strconv.FormatInt(int64(v.(int)), 10))
	case float64:
		rslt.WriteString(strconv.FormatFloat(v.(float64), 'f', -1, 64))
	case KV:
		fKV(rslt, v.(KV))
	case Slc:
		fSlc(rslt, v.(Slc))
	default:
		println("unsupported type")
	}
}

type (
	KV  map[string]interface{}
	Slc []interface{}
)

func main() {
	kv := KV{
		"a": 123,
		"b": Slc{1, 2},
		"c": 1.23,
		"d": Slc{1.2, 2.3},
		"e": KV{"a": 123},
		"f": Slc{KV{"a": 12}, KV{"b": 23}},
		"g": "abc",
		"h": Slc{"ab", "bc"},
	}
	var rslt bytes.Buffer
	Marshal(&rslt, kv)
	println(rslt.String())
}