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Published: Dec 6, 2019 License: BSD-3-Clause Imports: 5 Imported by: 372


structtag GoDoc

structtag provides an easy way of parsing and manipulating struct tag fields. Please vendor the library as it might change in future versions.


go get


package main

import (


func main() {
	type t struct {
		t string `json:"foo,omitempty,string" xml:"foo"`

	// get field tag
	tag := reflect.TypeOf(t{}).Field(0).Tag

	// ... and start using structtag by parsing the tag
	tags, err := structtag.Parse(string(tag))
	if err != nil {

	// iterate over all tags
	for _, t := range tags.Tags() {
		fmt.Printf("tag: %+v\n", t)

	// get a single tag
	jsonTag, err := tags.Get("json")
	if err != nil {
	fmt.Println(jsonTag)         // Output: json:"foo,omitempty,string"
	fmt.Println(jsonTag.Key)     // Output: json
	fmt.Println(jsonTag.Name)    // Output: foo
	fmt.Println(jsonTag.Options) // Output: [omitempty string]

	// change existing tag
	jsonTag.Name = "foo_bar"
	jsonTag.Options = nil

	// add new tag
		Key:     "hcl",
		Name:    "foo",
		Options: []string{"squash"},

	// print the tags
	fmt.Println(tags) // Output: json:"foo_bar" xml:"foo" hcl:"foo,squash"

	// sort tags according to keys
	fmt.Println(tags) // Output: hcl:"foo,squash" json:"foo_bar" xml:"foo"




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type Tag

type Tag struct {
	// Key is the tag key, such as json, xml, etc..
	// i.e: `json:"foo,omitempty". Here key is: "json"
	Key string

	// Name is a part of the value
	// i.e: `json:"foo,omitempty". Here name is: "foo"
	Name string

	// Options is a part of the value. It contains a slice of tag options i.e:
	// `json:"foo,omitempty". Here options is: ["omitempty"]
	Options []string

Tag defines a single struct's string literal tag

func (*Tag) GoString

func (t *Tag) GoString() string

GoString implements the fmt.GoStringer interface

func (*Tag) HasOption

func (t *Tag) HasOption(opt string) bool

HasOption returns true if the given option is available in options

func (*Tag) String

func (t *Tag) String() string

String reassembles the tag into a valid tag field representation

func (*Tag) Value added in v0.2.0

func (t *Tag) Value() string

Value returns the raw value of the tag, i.e. if the tag is `json:"foo,omitempty", the Value is "foo,omitempty"

type Tags

type Tags struct {
	// contains filtered or unexported fields

Tags represent a set of tags from a single struct field

func Parse

func Parse(tag string) (*Tags, error)

Parse parses a single struct field tag and returns the set of tags.

func (*Tags) AddOptions

func (t *Tags) AddOptions(key string, options ...string)

AddOptions adds the given option for the given key. If the option already exists it doesn't add it again.

func (*Tags) Delete

func (t *Tags) Delete(keys ...string)

Delete deletes the tag for the given keys

func (*Tags) DeleteOptions

func (t *Tags) DeleteOptions(key string, options ...string)

DeleteOptions deletes the given options for the given key

func (*Tags) Get

func (t *Tags) Get(key string) (*Tag, error)

Get returns the tag associated with the given key. If the key is present in the tag the value (which may be empty) is returned. Otherwise the returned value will be the empty string. The ok return value reports whether the tag exists or not (which the return value is nil).

func (*Tags) Keys

func (t *Tags) Keys() []string

Tags returns a slice of tags. The order is the original tag order unless it was changed.

func (*Tags) Len

func (t *Tags) Len() int

func (*Tags) Less

func (t *Tags) Less(i int, j int) bool

func (*Tags) Set

func (t *Tags) Set(tag *Tag) error

Set sets the given tag. If the tag key already exists it'll override it

func (*Tags) String

func (t *Tags) String() string

String reassembles the tags into a valid literal tag field representation

func (*Tags) Swap

func (t *Tags) Swap(i int, j int)

func (*Tags) Tags

func (t *Tags) Tags() []*Tag

Tags returns a slice of tags. The order is the original tag order unless it was changed.

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