jsonmap

Ordered map

Simple ordered map for Go, with JSON restrictions. The main purpose is to keep same order of keys after parsing JSON and generating it again, so Unmarshal followed by Marshal generates exactly the same JSON structure

Keys are strings, Values are any JSON values (number, string, boolean, null, array, map/object)

Storage is O(n), operations are O(1), except for optional operations in slow.go file

When Unmarshalling, any nested map from JSON is created as ordered, including maps in nested arrays

Alternative implementation is in simplemap, it has simple structure, O(1) Keys, but O(n) Delete operation. Check the difference by running go test -v -bench=. -benchmem

Inspired by wk8/go-ordered-map and iancoleman/orderedmap

Usage

package main

import (
	"encoding/json"
	"fmt"

	"github.com/metalim/jsonmap"
	// or simpler alternative, but with O(n) Delete()
	// jsonmap "github.com/metalim/jsonmap/simplemap"
)

const input = `{"an":"article","empty":null,"sub":{"s":1,"e":2,"x":3,"y":4},"bool":false,"array":[1,2,3]}`

func main() {
	m := jsonmap.New()

	// unmarshal, keeping order
	err := json.Unmarshal([]byte(input), &m)
	if err != nil {
		panic(err)
	}

	// get values
	val, ok := m.Get("an")
	fmt.Println("an: ", val, ok) // article true
	val, ok = m.Get("non-existant")
	fmt.Println("non-existant", val, ok) // <nil> false

	// marshal, keeping order
	output, err := json.Marshal(&m)
	if err != nil {
		panic(err)
	}

	if string(output) == input {
		fmt.Println("output == input")
	}

	// iterate
	fmt.Println("forward order:")
	for el := m.First(); el != nil; el = el.Next() {
		fmt.Printf("\t%s: %v\n", el.Key(), el.Value())
	}
	fmt.Println()

	fmt.Println("backwards order:")
	for el := m.Last(); el != nil; el = el.Prev() {
		fmt.Printf("\t%s: %v\n", el.Key(), el.Value())
	}
	fmt.Println()

	fmt.Println(`forward from key "sub":`)
	for el := m.GetElement("sub"); el != nil; el = el.Next() {
		fmt.Printf("\t%s: %v\n", el.Key(), el.Value())
	}
	fmt.Println()

	// print map
	fmt.Println(m) // map[an:article empty:<nil> sub:map[s:1 e:2 x:3 y:4] bool:false array:[1 2 3]]

	// set new values, keeping order of existing keys
	m.Set("an", "bar")
	m.Set("truth", true)
	fmt.Println(m) // map[an:bar empty:<nil> sub:map[s:1 e:2 x:3 y:4] bool:false array:[1 2 3] truth:true]

	// delete key "sub"
	m.Delete("sub")
	fmt.Println(m) // map[an:bar empty:<nil> bool:false array:[1 2 3] truth:true]

	// update value for key "an", and move it to the end
	m.Push("an", "end")
	fmt.Println(m) // map[empty:<nil> bool:false array:[1 2 3] truth:true an:end]

	data, err := json.Marshal(&m)
	if err != nil {
		panic(err)
	}
	fmt.Println(string(data)) // {"empty":null,"bool":false,"array":[1,2,3],"truth":true,"an":"end"}
}

Alternatives

• iancoleman/orderedmap — has O(n) time for Delete
• wk8/go-ordered-map — Unmarshal creates nested maps as vanilla unordered maps, which makes it useless for my purposes

Let me know of other alternatives, I'll add them here