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@lummie
Last active Jun 30, 2022
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What would you like to do?
Golang Enum pattern that can be serialized to json
package enum_example
import (
"bytes"
"encoding/json"
)
// TaskState represents the state of task, moving through Created, Running then Finished or Errorred
type TaskState int
const (
// Created represents the task has been created but not started yet
Created TaskState = iota
//Running represents the task has started
Running
// Finished represents the task is complete
Finished
// Errorred represents the task has encountered a problem and is no longer running
Errorred
)
func (s TaskState) String() string {
return toString[s]
}
var toString = map[TaskState]string{
Created: "Created",
Running: "Running",
Finished: "Finished",
Errorred: "Errorred",
}
var toID = map[string]TaskState{
"Created": Created,
"Running": Running,
"Finished": Finished,
"Errorred": Errorred,
}
// MarshalJSON marshals the enum as a quoted json string
func (s TaskState) MarshalJSON() ([]byte, error) {
buffer := bytes.NewBufferString(`"`)
buffer.WriteString(toString[s])
buffer.WriteString(`"`)
return buffer.Bytes(), nil
}
// UnmarshalJSON unmashals a quoted json string to the enum value
func (s *TaskState) UnmarshalJSON(b []byte) error {
var j string
err := json.Unmarshal(b, &j)
if err != nil {
return err
}
// Note that if the string cannot be found then it will be set to the zero value, 'Created' in this case.
*s = toID[j]
return nil
}
@tonyalaribe
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tonyalaribe commented Jun 16, 2018

WOW. Thanks for this.

@nilskuhn
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nilskuhn commented Aug 26, 2018

Really helpful, thanks for sharing!

@mbana
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mbana commented Nov 22, 2018

Cheers

@wgfm
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wgfm commented Nov 28, 2018

For me, MarshalJSON only works when its receiver is a TaskState, rather than a *TaskState:

func (s TaskState) MarshalJSON() ([]byte, error)

@lummie
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Author

lummie commented Dec 11, 2018

For me, MarshalJSON only works when its receiver is a TaskState, rather than a *TaskState:

Good spot, thanks I'd replaced the original gist with a cleaner example and introduced that bug 😛
Gist fixed.

@soolaugust
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soolaugust commented Mar 28, 2019

Very Cool, 👍

@dvasilen
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dvasilen commented May 2, 2019

Thanks, very helpful!

@xyalan
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xyalan commented Jul 9, 2019

cool

@nohwnd
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nohwnd commented Jul 12, 2019

Very useful, thanks. It is also nice to know that editors support regex replace which allows you to generate the contents of toString and toId very easily from the list of enum values.

For example toString can be generated by copying the list of values, and doing this regex replacement on it:
find: (\w+).*
replace with: $1: "$1"

@difficultwork
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difficultwork commented Oct 24, 2019

So cooooool👍

@bhansconnect
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bhansconnect commented Nov 21, 2019

Another option is:

type TaskState string

const (

	// Created represents the task has been created but not started yet

	Created TaskState = "Created"

	//Running represents the task has started

	Running = "Running"

	// Finished represents the task is complete

	Finished = "Finished"

	// Errorred represents the task has encountered a problem and is no longer running

	Errorred ="Errored"

)

The one disadvantage is that if you do a bunch a comparisons in Go, they will be string comparisons instead of int. This could effect performance, but for most cases is probably insignificant.

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ghost commented Jul 6, 2020

Thank you!

@sylv-io
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sylv-io commented Sep 1, 2020

thanks 👍

@hznut
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hznut commented Sep 16, 2021

Thanks!

@subutux
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subutux commented Oct 1, 2021

my two cents:

type Kind int

const (
	Sent Kind = iota
	Received
	Failed
	Report
)

func (t Kind) String() string {
	return [...]string{"Sent", "Received", "Failed", "Report"}[t]
}

func (t *Kind) FromString(kind string) Kind {
	return map[string]Kind{
		"Sent":     Sent,
		"Received": Received,
		"Failed":   Failed,
		"Report":   Report,
	}[kind]
}

func (t Kind) MarshalJSON() ([]byte, error) {
	return json.Marshal(t.String())
}

func (t *Kind) UnMarshalJSON(b []byte) error {
	var s string
	err := json.Unmarshal(b, &s)
	if err != nil {
		return err
	}
	*t = t.FromString(s)
	return nil
}

@alex21289
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alex21289 commented Oct 29, 2021

my two cents:

type Kind int

const (
	Sent Kind = iota
	Received
	Failed
	Report
)

func (t Kind) String() string {
	return [...]string{"Sent", "Received", "Failed", "Report"}[t]
}

func (t *Kind) FromString(kind string) Kind {
	return map[string]Kind{
		"Sent":     Sent,
		"Received": Received,
		"Failed":   Failed,
		"Report":   Report,
	}[kind]
}

func (t Kind) MarshalJSON() ([]byte, error) {
	return json.Marshal(t.String())
}

func (t *Kind) UnMarshalJSON(b []byte) error {
	var s string
	err := json.Unmarshal(b, &s)
	if err != nil {
		return err
	}
	*t = t.FromString(s)
	return nil
}

Nice, the same approach comes to my mind. When you put the maps in a function they are immutable. I think that is a better approach.

Thank you, for this example.

@jaxsong
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jaxsong commented Dec 27, 2021

type Kind int

const (
	Unknown Kind = iota
	Sent
	Received
	Failed
	Report
)

func (t Kind) String() string {
	return [...]string{"Unknown", "Sent", "Received", "Failed", "Report"}[t]
}

func (t *Kind) FromString(kind string) Kind {
	return map[string]Kind{
		"Unknown":  Unknown,
		"Sent":     Sent,
		"Received": Received,
		"Failed":   Failed,
		"Report":   Report,
	}[kind]
}

func (t Kind) MarshalJSON() ([]byte, error) {
	return json.Marshal(t.String())
}

func (t *Kind) UnmarshalJSON(b []byte) error {
	var s string
	err := json.Unmarshal(b, &s)
	if err != nil {
		return err
	}
	*t = t.FromString(s)
	return nil
}

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