去编译错误“未定义的函数”

Question

我有以下几段代码：接口及功能定义：package helperimport "gopkg.in/mgo.v2/bson"// Defines an interface for identifiable objectstype Identifiable interface {    GetIdentifier() bson.ObjectId}// Checks if a slice contains a given object with a given bson.ObjectIdfunc IsInSlice(id bson.ObjectId, objects []Identifiable) bool {    for _, single := range objects {        if single.GetIdentifier() == id {            return true        }    }    return false}满足“可识别”的用户结构的定义：package modelsimport (    "github.com/my/project/services"    "gopkg.in/mgo.v2/bson")type User struct {    Id       bson.ObjectId   `json:"_id,omitempty" bson:"_id,omitempty"`    Username string          `json:"username" bson:"username"`    Email    string          `json:"email" bson:"email"`    Password string          `json:"password" bson:"password"`    Albums   []bson.ObjectId `json:"albums,omitempty" bson:"albums,omitempty"`    Friends  []bson.ObjectId `json:"friends,omitempty" bson:"friends,omitempty"`}func GetUserById(id string) (err error, user *User) {    dbConnection, dbCollection := services.GetDbConnection("users")    defer dbConnection.Close()    err = dbCollection.Find(bson.M{"_id": bson.ObjectIdHex(id)}).One(&user)    return err, user}func (u *User) GetIdentifier() bson.ObjectId {    return u.Id}检查切片内对象是否存在的测试：package controllersimport (     "github.com/my/project/helper"    "gopkg.in/mgo.v2/bson")var testerId = bson.NewObjectId()var users = []models.Users{}/* Some code to get users from db */if !helper.IsInSlice(testerId, users) {    t.Fatalf("User is not saved in the database")}当我尝试编译测试时，我收到错误：undefined helper.IsInSlice. 当我重写IsInSlice方法以不采取[]Identifiable但[]models.User它工作正常。有任何想法吗？

Answer 1

您的问题是您试图将 type[]models.Users{}的值用作type的值[]Identifiable。当models.Usersimplements 时Identifiable，Go 的类型系统被设计成实现接口的值的切片不能用作（或转换为）接口类型的切片。

有关更多详细信息，请参阅 Go 规范关于转换的部分。