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proposal: encoding/json: add interface for omitempty #32675

MrTravisB opened this issue Jun 18, 2019 · 1 comment

proposal: encoding/json: add interface for omitempty #32675

MrTravisB opened this issue Jun 18, 2019 · 1 comment


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It would be nice to be able to omit objects from encoding that are of some custom type. For instance

type Name struct {
	First string `json:"first,omitempty"`
	Last string `json:"last,omitempty"`

type Person struct {
	Name Name `json:"name,omitempty"`
	Age int `json:"age"`

p := Person{
	Age: 42,
b, _ := json.Marshal(p)

Ideally that would print


but instead it prints


What would be nice would be to have an interface, json.Empty, which could be used to determine if the value is empty or not.

type Empty interface {
	IsEmpty() bool

func (n Name) IsEmpty() bool {
	return n.First == "" && n.Last == ""

The check for this could then just be another case added to json.isEmptyValue()

if emp, ok := v.Interface().(Empty); ok {
	return emp.IsEmpty()
@gopherbot gopherbot added this to the Proposal milestone Jun 18, 2019
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Duplicate of #11939.

And I guess you already knew, but just wanted to put it out there - if you change Name to a pointer like

Name *Name `json:"name,omitempty"`

"name": {} goes away.

@golang golang locked and limited conversation to collaborators Jun 18, 2020
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