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@lummie
Last active Aug 1, 2022
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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
}
@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
}

@adev73
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adev73 commented Jul 14, 2022

func (t *Kind) UnMarshalJSON(b []byte) error {

Note that this should be UnmarshalJSON, without the capital "M" in the middle... other than that, works brilliantly, thanks!

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