1# Mergo
2
3[![GitHub release][5]][6]
4[![GoCard][7]][8]
5[![Test status][1]][2]
6[![OpenSSF Scorecard][21]][22]
7[![OpenSSF Best Practices][19]][20]
8[![Coverage status][9]][10]
9[![Sourcegraph][11]][12]
10[![FOSSA status][13]][14]
11
12[![GoDoc][3]][4]
13[![Become my sponsor][15]][16]
14[![Tidelift][17]][18]
15
16[1]: https://github.com/imdario/mergo/workflows/tests/badge.svg?branch=master
17[2]: https://github.com/imdario/mergo/actions/workflows/tests.yml
18[3]: https://godoc.org/github.com/imdario/mergo?status.svg
19[4]: https://godoc.org/github.com/imdario/mergo
20[5]: https://img.shields.io/github/release/imdario/mergo.svg
21[6]: https://github.com/imdario/mergo/releases
22[7]: https://goreportcard.com/badge/imdario/mergo
23[8]: https://goreportcard.com/report/github.com/imdario/mergo
24[9]: https://coveralls.io/repos/github/imdario/mergo/badge.svg?branch=master
25[10]: https://coveralls.io/github/imdario/mergo?branch=master
26[11]: https://sourcegraph.com/github.com/imdario/mergo/-/badge.svg
27[12]: https://sourcegraph.com/github.com/imdario/mergo?badge
28[13]: https://app.fossa.io/api/projects/git%2Bgithub.com%2Fimdario%2Fmergo.svg?type=shield
29[14]: https://app.fossa.io/projects/git%2Bgithub.com%2Fimdario%2Fmergo?ref=badge_shield
30[15]: https://img.shields.io/github/sponsors/imdario
31[16]: https://github.com/sponsors/imdario
32[17]: https://tidelift.com/badges/package/go/github.com%2Fimdario%2Fmergo
33[18]: https://tidelift.com/subscription/pkg/go-github.com-imdario-mergo
34[19]: https://bestpractices.coreinfrastructure.org/projects/7177/badge
35[20]: https://bestpractices.coreinfrastructure.org/projects/7177
36[21]: https://api.securityscorecards.dev/projects/github.com/imdario/mergo/badge
37[22]: https://api.securityscorecards.dev/projects/github.com/imdario/mergo
38
39A helper to merge structs and maps in Golang. Useful for configuration default values, avoiding messy if-statements.
40
41Mergo merges same-type structs and maps by setting default values in zero-value fields. Mergo won't merge unexported (private) fields. It will do recursively any exported one. It also won't merge structs inside maps (because they are not addressable using Go reflection).
42
43Also a lovely [comune](http://en.wikipedia.org/wiki/Mergo) (municipality) in the Province of Ancona in the Italian region of Marche.
44
45## Status
46
47It is ready for production use. [It is used in several projects by Docker, Google, The Linux Foundation, VMWare, Shopify, Microsoft, etc](https://github.com/imdario/mergo#mergo-in-the-wild).
48
49### Important notes
50
51#### 1.0.0
52
53In [1.0.0](//github.com/imdario/mergo/releases/tag/1.0.0) Mergo moves to a vanity URL `dario.cat/mergo`.
54
55#### 0.3.9
56
57Please keep in mind that a problematic PR broke [0.3.9](//github.com/imdario/mergo/releases/tag/0.3.9). I reverted it in [0.3.10](//github.com/imdario/mergo/releases/tag/0.3.10), and I consider it stable but not bug-free. Also, this version adds support for go modules.
58
59Keep in mind that in [0.3.2](//github.com/imdario/mergo/releases/tag/0.3.2), Mergo changed `Merge()`and `Map()` signatures to support [transformers](#transformers). I added an optional/variadic argument so that it won't break the existing code.
60
61If you were using Mergo before April 6th, 2015, please check your project works as intended after updating your local copy with ```go get -u dario.cat/mergo```. I apologize for any issue caused by its previous behavior and any future bug that Mergo could cause in existing projects after the change (release 0.2.0).
62
63### Donations
64
65If Mergo is useful to you, consider buying me a coffee, a beer, or making a monthly donation to allow me to keep building great free software. :heart_eyes:
66
67<a href='https://ko-fi.com/B0B58839' target='_blank'><img height='36' style='border:0px;height:36px;' src='https://az743702.vo.msecnd.net/cdn/kofi1.png?v=0' border='0' alt='Buy Me a Coffee at ko-fi.com' /></a>
68<a href="https://liberapay.com/dario/donate"><img alt="Donate using Liberapay" src="https://liberapay.com/assets/widgets/donate.svg"></a>
69<a href='https://github.com/sponsors/imdario' target='_blank'><img alt="Become my sponsor" src="https://img.shields.io/github/sponsors/imdario?style=for-the-badge" /></a>
70
71### Mergo in the wild
72
73- [moby/moby](https://github.com/moby/moby)
74- [kubernetes/kubernetes](https://github.com/kubernetes/kubernetes)
75- [vmware/dispatch](https://github.com/vmware/dispatch)
76- [Shopify/themekit](https://github.com/Shopify/themekit)
77- [imdario/zas](https://github.com/imdario/zas)
78- [matcornic/hermes](https://github.com/matcornic/hermes)
79- [OpenBazaar/openbazaar-go](https://github.com/OpenBazaar/openbazaar-go)
80- [kataras/iris](https://github.com/kataras/iris)
81- [michaelsauter/crane](https://github.com/michaelsauter/crane)
82- [go-task/task](https://github.com/go-task/task)
83- [sensu/uchiwa](https://github.com/sensu/uchiwa)
84- [ory/hydra](https://github.com/ory/hydra)
85- [sisatech/vcli](https://github.com/sisatech/vcli)
86- [dairycart/dairycart](https://github.com/dairycart/dairycart)
87- [projectcalico/felix](https://github.com/projectcalico/felix)
88- [resin-os/balena](https://github.com/resin-os/balena)
89- [go-kivik/kivik](https://github.com/go-kivik/kivik)
90- [Telefonica/govice](https://github.com/Telefonica/govice)
91- [supergiant/supergiant](supergiant/supergiant)
92- [SergeyTsalkov/brooce](https://github.com/SergeyTsalkov/brooce)
93- [soniah/dnsmadeeasy](https://github.com/soniah/dnsmadeeasy)
94- [ohsu-comp-bio/funnel](https://github.com/ohsu-comp-bio/funnel)
95- [EagerIO/Stout](https://github.com/EagerIO/Stout)
96- [lynndylanhurley/defsynth-api](https://github.com/lynndylanhurley/defsynth-api)
97- [russross/canvasassignments](https://github.com/russross/canvasassignments)
98- [rdegges/cryptly-api](https://github.com/rdegges/cryptly-api)
99- [casualjim/exeggutor](https://github.com/casualjim/exeggutor)
100- [divshot/gitling](https://github.com/divshot/gitling)
101- [RWJMurphy/gorl](https://github.com/RWJMurphy/gorl)
102- [andrerocker/deploy42](https://github.com/andrerocker/deploy42)
103- [elwinar/rambler](https://github.com/elwinar/rambler)
104- [tmaiaroto/gopartman](https://github.com/tmaiaroto/gopartman)
105- [jfbus/impressionist](https://github.com/jfbus/impressionist)
106- [Jmeyering/zealot](https://github.com/Jmeyering/zealot)
107- [godep-migrator/rigger-host](https://github.com/godep-migrator/rigger-host)
108- [Dronevery/MultiwaySwitch-Go](https://github.com/Dronevery/MultiwaySwitch-Go)
109- [thoas/picfit](https://github.com/thoas/picfit)
110- [mantasmatelis/whooplist-server](https://github.com/mantasmatelis/whooplist-server)
111- [jnuthong/item_search](https://github.com/jnuthong/item_search)
112- [bukalapak/snowboard](https://github.com/bukalapak/snowboard)
113- [containerssh/containerssh](https://github.com/containerssh/containerssh)
114- [goreleaser/goreleaser](https://github.com/goreleaser/goreleaser)
115- [tjpnz/structbot](https://github.com/tjpnz/structbot)
116
117## Install
118
119 go get dario.cat/mergo
120
121 // use in your .go code
122 import (
123 "dario.cat/mergo"
124 )
125
126## Usage
127
128You can only merge same-type structs with exported fields initialized as zero value of their type and same-types maps. Mergo won't merge unexported (private) fields but will do recursively any exported one. It won't merge empty structs value as [they are zero values](https://golang.org/ref/spec#The_zero_value) too. Also, maps will be merged recursively except for structs inside maps (because they are not addressable using Go reflection).
129
130```go
131if err := mergo.Merge(&dst, src); err != nil {
132 // ...
133}
134```
135
136Also, you can merge overwriting values using the transformer `WithOverride`.
137
138```go
139if err := mergo.Merge(&dst, src, mergo.WithOverride); err != nil {
140 // ...
141}
142```
143
144Additionally, you can map a `map[string]interface{}` to a struct (and otherwise, from struct to map), following the same restrictions as in `Merge()`. Keys are capitalized to find each corresponding exported field.
145
146```go
147if err := mergo.Map(&dst, srcMap); err != nil {
148 // ...
149}
150```
151
152Warning: if you map a struct to map, it won't do it recursively. Don't expect Mergo to map struct members of your struct as `map[string]interface{}`. They will be just assigned as values.
153
154Here is a nice example:
155
156```go
157package main
158
159import (
160 "fmt"
161 "dario.cat/mergo"
162)
163
164type Foo struct {
165 A string
166 B int64
167}
168
169func main() {
170 src := Foo{
171 A: "one",
172 B: 2,
173 }
174 dest := Foo{
175 A: "two",
176 }
177 mergo.Merge(&dest, src)
178 fmt.Println(dest)
179 // Will print
180 // {two 2}
181}
182```
183
184Note: if test are failing due missing package, please execute:
185
186 go get gopkg.in/yaml.v3
187
188### Transformers
189
190Transformers allow to merge specific types differently than in the default behavior. In other words, now you can customize how some types are merged. For example, `time.Time` is a struct; it doesn't have zero value but IsZero can return true because it has fields with zero value. How can we merge a non-zero `time.Time`?
191
192```go
193package main
194
195import (
196 "fmt"
197 "dario.cat/mergo"
198 "reflect"
199 "time"
200)
201
202type timeTransformer struct {
203}
204
205func (t timeTransformer) Transformer(typ reflect.Type) func(dst, src reflect.Value) error {
206 if typ == reflect.TypeOf(time.Time{}) {
207 return func(dst, src reflect.Value) error {
208 if dst.CanSet() {
209 isZero := dst.MethodByName("IsZero")
210 result := isZero.Call([]reflect.Value{})
211 if result[0].Bool() {
212 dst.Set(src)
213 }
214 }
215 return nil
216 }
217 }
218 return nil
219}
220
221type Snapshot struct {
222 Time time.Time
223 // ...
224}
225
226func main() {
227 src := Snapshot{time.Now()}
228 dest := Snapshot{}
229 mergo.Merge(&dest, src, mergo.WithTransformers(timeTransformer{}))
230 fmt.Println(dest)
231 // Will print
232 // { 2018-01-12 01:15:00 +0000 UTC m=+0.000000001 }
233}
234```
235
236## Contact me
237
238If I can help you, you have an idea or you are using Mergo in your projects, don't hesitate to drop me a line (or a pull request): [@im_dario](https://twitter.com/im_dario)
239
240## About
241
242Written by [Dario Castañé](http://dario.im).
243
244## License
245
246[BSD 3-Clause](http://opensource.org/licenses/BSD-3-Clause) license, as [Go language](http://golang.org/LICENSE).
247
248[](https://app.fossa.io/projects/git%2Bgithub.com%2Fimdario%2Fmergo?ref=badge_large)
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