将 JSON 解码为接口值

Question

由于 encoding/json 需要一个非 nil 接口来解组：我如何可靠地制作用户提供的指针类型的（完整）副本，将其存储在我的User接口中，然后 JSON 解码为该临时？注意：这里的目标是实现“无人值守”——即从 Redis/BoltDB 中提取字节，解码为接口类型，然后检查GetID()接口定义的方法是否返回非空字符串，以及请求中间件。游乐场：http : //play.golang.org/p/rYODiNrfWwpackage mainimport (    "bytes"    "encoding/json"    "fmt"    "log"    "net/http"    "os"    "time")type session struct {    ID      string    User    User    Expires int64}type User interface {    GetID() string}type LocalUser struct {    ID      string    Name    string    Created time.Time}func (u *LocalUser) GetID() string {    return u.ID}type Auth struct {    key []byte    // We store an instance of userType here so we can unmarshal into it when    // deserializing from JSON (or other non-gob decoders) into *session.User.    // Attempting to unmarshal into a nil session.User would otherwise fail.    // We do this so we can unmarshal from our data-store per-request *without    // the package user having to do so manually* in the HTTP middleware. We can't    // rely on the user passing in an fresh instance of their User satisfying type.    userType User}func main() {    // auth is a pointer to avoid copying the struct per-request: although small    // here, it contains a 32-byte key, options fields, etc. outside of this example.    var auth = &Auth{key: []byte("abc")}    local := &LocalUser{"19313", "Matt", time.Now()}    b, _, _, err := auth.SetUser(local)    if err != nil {        log.Fatalf("SetUser: %v", err)    }    user, err := auth.GetUser(b)    if err != nil {        log.Fatalf("GetUser: %#v", err)    }    fmt.Fprintf(os.Stdout, "%v\n", user)}

Answer 1

如果您需要深度复制接口，请将该方法添加到您的接口中。

type User interface {

  GetID() string

  Copy() User

}

type LocalUser struct {

  ID string

  Name string

  Created time.Time

}

// Copy receives a copy of LocalUser and returns a pointer to it.

func (u LocalUser) Copy() User {

  return &u

}

Answer 2

因为应用程序将解码为 aUser并且 JSON 解码器的参数必须是指针值，所以我们可以假设User值是指针值。鉴于此假设，以下代码可用于为解码创建新的零值：

uzero := reflect.New(reflect.TypeOf(u).Elem()).Interface().(User)