package module
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Published: Aug 9, 2023 License: MIT Imports: 8 Imported by: 2,141



I am a copier, I copy everything from one to another

test status


  • Copy from field to field with same name
  • Copy from method to field with same name
  • Copy from field to method with same name
  • Copy from slice to slice
  • Copy from struct to slice
  • Copy from map to map
  • Enforce copying a field with a tag
  • Ignore a field with a tag
  • Deep Copy


package main

import (

type User struct {
	Name        string
	Role        string
	Age         int32
	EmployeeCode int64 `copier:"EmployeeNum"` // specify field name

	// Explicitly ignored in the destination struct.
	Salary   int

func (user *User) DoubleAge() int32 {
	return 2 * user.Age

// Tags in the destination Struct provide instructions to copier.Copy to ignore
// or enforce copying and to panic or return an error if a field was not copied.
type Employee struct {
	// Tell copier.Copy to panic if this field is not copied.
	Name      string `copier:"must"`

	// Tell copier.Copy to return an error if this field is not copied.
	Age       int32  `copier:"must,nopanic"`

	// Tell copier.Copy to explicitly ignore copying this field.
	Salary    int    `copier:"-"`

	DoubleAge int32
	EmployeeId int64 `copier:"EmployeeNum"` // specify field name
	SuperRole string

func (employee *Employee) Role(role string) {
	employee.SuperRole = "Super " + role

func main() {
	var (
		user      = User{Name: "Jinzhu", Age: 18, Role: "Admin", Salary: 200000}
		users     = []User{{Name: "Jinzhu", Age: 18, Role: "Admin", Salary: 100000}, {Name: "jinzhu 2", Age: 30, Role: "Dev", Salary: 60000}}
		employee  = Employee{Salary: 150000}
		employees = []Employee{}

	copier.Copy(&employee, &user)

	fmt.Printf("%#v \n", employee)
	// Employee{
	//    Name: "Jinzhu",           // Copy from field
	//    Age: 18,                  // Copy from field
	//    Salary:150000,            // Copying explicitly ignored
	//    DoubleAge: 36,            // Copy from method
	//    EmployeeId: 0,            // Ignored
	//    SuperRole: "Super Admin", // Copy to method
	// }

	// Copy struct to slice
	copier.Copy(&employees, &user)

	fmt.Printf("%#v \n", employees)
	// []Employee{
	//   {Name: "Jinzhu", Age: 18, Salary:0, DoubleAge: 36, EmployeeId: 0, SuperRole: "Super Admin"}
	// }

	// Copy slice to slice
	employees = []Employee{}
	copier.Copy(&employees, &users)

	fmt.Printf("%#v \n", employees)
	// []Employee{
	//   {Name: "Jinzhu", Age: 18, Salary:0, DoubleAge: 36, EmployeeId: 0, SuperRole: "Super Admin"},
	//   {Name: "jinzhu 2", Age: 30, Salary:0, DoubleAge: 60, EmployeeId: 0, SuperRole: "Super Dev"},
	// }

 	// Copy map to map
	map1 := map[int]int{3: 6, 4: 8}
	map2 := map[int32]int8{}
	copier.Copy(&map2, map1)

	fmt.Printf("%#v \n", map2)
	// map[int32]int8{3:6, 4:8}
Copy with Option
copier.CopyWithOption(&to, &from, copier.Option{IgnoreEmpty: true, DeepCopy: true})


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Released under the MIT License.




View Source
const (

	// Some default converter types for a nicer syntax
	String  string  = ""
	Bool    bool    = false
	Int     int     = 0
	Float32 float32 = 0
	Float64 float64 = 0

These flags define options for tag handling


View Source
var (
	ErrInvalidCopyDestination        = errors.New("copy destination must be non-nil and addressable")
	ErrInvalidCopyFrom               = errors.New("copy from must be non-nil and addressable")
	ErrMapKeyNotMatch                = errors.New("map's key type doesn't match")
	ErrNotSupported                  = errors.New("not supported")
	ErrFieldNameTagStartNotUpperCase = errors.New("copier field name tag must be start upper case")


func Copy

func Copy(toValue interface{}, fromValue interface{}) (err error)

Copy copy things

func CopyWithOption

func CopyWithOption(toValue interface{}, fromValue interface{}, opt Option) (err error)

CopyWithOption copy with option


type FieldNameMapping added in v0.4.0

type FieldNameMapping struct {
	SrcType interface{}
	DstType interface{}
	Mapping map[string]string

type Option

type Option struct {
	// setting this value to true will ignore copying zero values of all the fields, including bools, as well as a
	// struct having all it's fields set to their zero values respectively (see IsZero() in reflect/value.go)
	IgnoreEmpty   bool
	CaseSensitive bool
	DeepCopy      bool
	Converters    []TypeConverter
	// Custom field name mappings to copy values with different names in `fromValue` and `toValue` types.
	// Examples can be found in `copier_field_name_mapping_test.go`.
	FieldNameMapping []FieldNameMapping

Option sets copy options

type TypeConverter added in v0.3.5

type TypeConverter struct {
	SrcType interface{}
	DstType interface{}
	Fn      func(src interface{}) (dst interface{}, err error)

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