package mainimport ( "errors" "fmt" "log" "reflect" "time")type User struct { ID int `json:"id"` Username string `json:"username"` about string `json:"about"` IsAdmin bool `json:"is_admin"` Status int `json:"status"` Date *time.Time}func main() { now := time.Now() ua := User{ ID: 1, Username: "admin", about: "I am an admin", IsAdmin: true, Status: 1, Date: &now, } ub := User{ Username: "user", } fmt.Printf("ua: %+vn", ua) fmt.Printf("ub: %+vn", ub) err := Replace(ua, &ub) if err != nil { log.Fatal(err) } fmt.Printf("nua: %+vn", ua) fmt.Printf("ub: %+vn", ub)}// IsZeroOfUnderlyingType return wether x is the is// the zero-value of its underlying type.func IsZeroOfUnderlyingType(x interface{}) bool { return reflect.DeepEqual(x, reflect.Zero(reflect.TypeOf(x)).Interface())}// Replace replaces all fields of struct b that have a// zero-value with the corresponding field value from a.// b must be a pointer to a struct.func Replace(a, b interface{}) error { // Check a. va := reflect.ValueOf(a) if va.Kind() != reflect.Struct { return errors.New("a is not a struct") } // Check b. vb := reflect.ValueOf(b) if vb.Kind() != reflect.Ptr { return errors.New("b is not a pointer") } // vb is a pointer, indirect it to get the // underlying value, and make sure it is a struct. vb = vb.Elem() if vb.Kind() != reflect.Struct { return errors.New("b is not a struct") } for i := 0; i < vb.NumField(); i++ { field := vb.Field(i) if field.CanInterface() && IsZeroOfUnderlyingType(field.Interface()) { // This field have a zero-value. // Search in a for a field with the same name. name := vb.Type().Field(i).Name fa := va.FieldByName(name) if fa.IsValid() { // Field with name was found in struct a, // assign its value to the field in b. if field.CanSet() { field.Set(fa) } } } } return nil}输出量
ua: {ID:1 Username:admin about:I am an admin IsAdmin:true Status:1 Date:2017-05-11 17:47:30.805657327 +0200 CEST}ub: {ID:0 Username:user about: IsAdmin:false Status:0 Date:<nil>}ua: {ID:1 Username:admin about:I am an admin IsAdmin:true Status:1 Date:2017-05-11 17:47:30.805657327 +0200 CEST}ub: {ID:1 Username:user about:I am an admin IsAdmin:true Status:1 Date:2017-05-11 17:47:30.805657327 +0200 CEST}
