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Matteo Scandoloa4285862020-12-01 18:10:10 -08001// Copyright 2013 Dario Castañé. All rights reserved.
2// Copyright 2009 The Go Authors. All rights reserved.
3// Use of this source code is governed by a BSD-style
4// license that can be found in the LICENSE file.
5
6/*
7A helper to merge structs and maps in Golang. Useful for configuration default values, avoiding messy if-statements.
8
9Mergo 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).
10
11Status
12
13It is ready for production use. It is used in several projects by Docker, Google, The Linux Foundation, VMWare, Shopify, etc.
14
15Important note
16
17Please keep in mind that a problematic PR broke 0.3.9. We reverted it in 0.3.10. We consider 0.3.10 as stable but not bug-free. . Also, this version adds suppot for go modules.
18
19Keep in mind that in 0.3.2, Mergo changed Merge() and Map() signatures to support transformers. We added an optional/variadic argument so that it won't break the existing code.
20
21If 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 in existing projects after the change (release 0.2.0).
22
23Install
24
25Do your usual installation procedure:
26
27 go get github.com/imdario/mergo
28
29 // use in your .go code
30 import (
31 "github.com/imdario/mergo"
32 )
33
34Usage
35
36You 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 too. Also, maps will be merged recursively except for structs inside maps (because they are not addressable using Go reflection).
37
38 if err := mergo.Merge(&dst, src); err != nil {
39 // ...
40 }
41
42Also, you can merge overwriting values using the transformer WithOverride.
43
44 if err := mergo.Merge(&dst, src, mergo.WithOverride); err != nil {
45 // ...
46 }
47
48Additionally, 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.
49
50 if err := mergo.Map(&dst, srcMap); err != nil {
51 // ...
52 }
53
54Warning: 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.
55
56Here is a nice example:
57
58 package main
59
60 import (
61 "fmt"
62 "github.com/imdario/mergo"
63 )
64
65 type Foo struct {
66 A string
67 B int64
68 }
69
70 func main() {
71 src := Foo{
72 A: "one",
73 B: 2,
74 }
75 dest := Foo{
76 A: "two",
77 }
78 mergo.Merge(&dest, src)
79 fmt.Println(dest)
80 // Will print
81 // {two 2}
82 }
83
84Transformers
85
86Transformers 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?
87
88 package main
89
90 import (
91 "fmt"
92 "github.com/imdario/mergo"
93 "reflect"
94 "time"
95 )
96
97 type timeTransformer struct {
98 }
99
100 func (t timeTransformer) Transformer(typ reflect.Type) func(dst, src reflect.Value) error {
101 if typ == reflect.TypeOf(time.Time{}) {
102 return func(dst, src reflect.Value) error {
103 if dst.CanSet() {
104 isZero := dst.MethodByName("IsZero")
105 result := isZero.Call([]reflect.Value{})
106 if result[0].Bool() {
107 dst.Set(src)
108 }
109 }
110 return nil
111 }
112 }
113 return nil
114 }
115
116 type Snapshot struct {
117 Time time.Time
118 // ...
119 }
120
121 func main() {
122 src := Snapshot{time.Now()}
123 dest := Snapshot{}
124 mergo.Merge(&dest, src, mergo.WithTransformers(timeTransformer{}))
125 fmt.Println(dest)
126 // Will print
127 // { 2018-01-12 01:15:00 +0000 UTC m=+0.000000001 }
128 }
129
130Contact me
131
132If 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): https://twitter.com/im_dario
133
134About
135
136Written by Dario Castañé: https://da.rio.hn
137
138License
139
140BSD 3-Clause license, as Go language.
141
142*/
143package mergo