# Mergo A helper to merge structs and maps in Golang. Useful for configuration default values, avoiding messy if-statements. Also a lovely [comune](http://en.wikipedia.org/wiki/Mergo) (municipality) in the Province of Ancona in the Italian region of Marche. ## Status It is ready for production use. [It is used in several projects by Docker, Google, The Linux Foundation, VMWare, Shopify, etc](https://github.com/imdario/mergo#mergo-in-the-wild). [![GoDoc][3]][4] [![GoCard][5]][6] [![Build Status][1]][2] [![Coverage Status][7]][8] [![Sourcegraph][9]][10] [1]: https://travis-ci.org/imdario/mergo.png [2]: https://travis-ci.org/imdario/mergo [3]: https://godoc.org/github.com/imdario/mergo?status.svg [4]: https://godoc.org/github.com/imdario/mergo [5]: https://goreportcard.com/badge/imdario/mergo [6]: https://goreportcard.com/report/github.com/imdario/mergo [7]: https://coveralls.io/repos/github/imdario/mergo/badge.svg?branch=master [8]: https://coveralls.io/github/imdario/mergo?branch=master [9]: https://sourcegraph.com/github.com/imdario/mergo/-/badge.svg [10]: https://sourcegraph.com/github.com/imdario/mergo?badge ### Latest release [Release v0.3.6](https://github.com/imdario/mergo/releases/tag/v0.3.6). ### Important note Please keep 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). An optional/variadic argument has been added, so it won't break existing code. If you were using Mergo **before** April 6th 2015, please check your project works as intended after updating your local copy with ```go get -u github.com/imdario/mergo```. I apologize for any issue caused by its previous behavior and any future bug that Mergo could cause (I hope it won't!) in existing projects after the change (release 0.2.0). ### Donations If Mergo is useful to you, consider buying me a coffee, a beer or making a monthly donation so I can keep building great free software. :heart_eyes: <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> [![Beerpay](https://beerpay.io/imdario/mergo/badge.svg)](https://beerpay.io/imdario/mergo) [![Beerpay](https://beerpay.io/imdario/mergo/make-wish.svg)](https://beerpay.io/imdario/mergo) <a href="https://liberapay.com/dario/donate"><img alt="Donate using Liberapay" src="https://liberapay.com/assets/widgets/donate.svg"></a> ### Mergo in the wild - [moby/moby](https://github.com/moby/moby) - [kubernetes/kubernetes](https://github.com/kubernetes/kubernetes) - [vmware/dispatch](https://github.com/vmware/dispatch) - [Shopify/themekit](https://github.com/Shopify/themekit) - [imdario/zas](https://github.com/imdario/zas) - [matcornic/hermes](https://github.com/matcornic/hermes) - [OpenBazaar/openbazaar-go](https://github.com/OpenBazaar/openbazaar-go) - [kataras/iris](https://github.com/kataras/iris) - [michaelsauter/crane](https://github.com/michaelsauter/crane) - [go-task/task](https://github.com/go-task/task) - [sensu/uchiwa](https://github.com/sensu/uchiwa) - [ory/hydra](https://github.com/ory/hydra) - [sisatech/vcli](https://github.com/sisatech/vcli) - [dairycart/dairycart](https://github.com/dairycart/dairycart) - [projectcalico/felix](https://github.com/projectcalico/felix) - [resin-os/balena](https://github.com/resin-os/balena) - [go-kivik/kivik](https://github.com/go-kivik/kivik) - [Telefonica/govice](https://github.com/Telefonica/govice) - [supergiant/supergiant](supergiant/supergiant) - [SergeyTsalkov/brooce](https://github.com/SergeyTsalkov/brooce) - [soniah/dnsmadeeasy](https://github.com/soniah/dnsmadeeasy) - [ohsu-comp-bio/funnel](https://github.com/ohsu-comp-bio/funnel) - [EagerIO/Stout](https://github.com/EagerIO/Stout) - [lynndylanhurley/defsynth-api](https://github.com/lynndylanhurley/defsynth-api) - [russross/canvasassignments](https://github.com/russross/canvasassignments) - [rdegges/cryptly-api](https://github.com/rdegges/cryptly-api) - [casualjim/exeggutor](https://github.com/casualjim/exeggutor) - [divshot/gitling](https://github.com/divshot/gitling) - [RWJMurphy/gorl](https://github.com/RWJMurphy/gorl) - [andrerocker/deploy42](https://github.com/andrerocker/deploy42) - [elwinar/rambler](https://github.com/elwinar/rambler) - [tmaiaroto/gopartman](https://github.com/tmaiaroto/gopartman) - [jfbus/impressionist](https://github.com/jfbus/impressionist) - [Jmeyering/zealot](https://github.com/Jmeyering/zealot) - [godep-migrator/rigger-host](https://github.com/godep-migrator/rigger-host) - [Dronevery/MultiwaySwitch-Go](https://github.com/Dronevery/MultiwaySwitch-Go) - [thoas/picfit](https://github.com/thoas/picfit) - [mantasmatelis/whooplist-server](https://github.com/mantasmatelis/whooplist-server) - [jnuthong/item_search](https://github.com/jnuthong/item_search) - [bukalapak/snowboard](https://github.com/bukalapak/snowboard) ## Installation go get github.com/imdario/mergo // use in your .go code import ( "github.com/imdario/mergo" ) ## Usage You 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 not considered zero values](https://golang.org/ref/spec#The_zero_value) either. Also maps will be merged recursively except for structs inside maps (because they are not addressable using Go reflection). ```go if err := mergo.Merge(&dst, src); err != nil { // ... } ``` Also, you can merge overwriting values using the transformer `WithOverride`. ```go if err := mergo.Merge(&dst, src, mergo.WithOverride); err != nil { // ... } ``` Additionally, 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. ```go if err := mergo.Map(&dst, srcMap); err != nil { // ... } ``` Warning: 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. More information and examples in [godoc documentation](http://godoc.org/github.com/imdario/mergo). ### Nice example ```go package main import ( "fmt" "github.com/imdario/mergo" ) type Foo struct { A string B int64 } func main() { src := Foo{ A: "one", B: 2, } dest := Foo{ A: "two", } mergo.Merge(&dest, src) fmt.Println(dest) // Will print // {two 2} } ``` Note: if test are failing due missing package, please execute: go get gopkg.in/yaml.v2 ### Transformers Transformers 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`? ```go package main import ( "fmt" "github.com/imdario/mergo" "reflect" "time" ) type timeTransfomer struct { } func (t timeTransfomer) Transformer(typ reflect.Type) func(dst, src reflect.Value) error { if typ == reflect.TypeOf(time.Time{}) { return func(dst, src reflect.Value) error { if dst.CanSet() { isZero := dst.MethodByName("IsZero") result := isZero.Call([]reflect.Value{}) if result[0].Bool() { dst.Set(src) } } return nil } } return nil } type Snapshot struct { Time time.Time // ... } func main() { src := Snapshot{time.Now()} dest := Snapshot{} mergo.Merge(&dest, src, mergo.WithTransformers(timeTransfomer{})) fmt.Println(dest) // Will print // { 2018-01-12 01:15:00 +0000 UTC m=+0.000000001 } } ``` ## Contact me If 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) ## About Written by [Dario Castañé](http://dario.im). ## License [BSD 3-Clause](http://opensource.org/licenses/BSD-3-Clause) license, as [Go language](http://golang.org/LICENSE).