英文:
golang protobuf can not unmarshal in a generic type
问题
type Msg[T any] interface {
*T
proto.Message
}
func Handle[T any, U Msg[T]](cb func(req U) (proto.Message, error)) {
msg := new(T)
if err := proto.Unmarshal([]byte{}, msg); err != nil {
}
_, _ = cb(msg)
}
func main() {
Handle(doSomething)
}
func doSomething(req *pb.Hello) (proto.Message, error) {
_ = proto.Unmarshal([]byte{}, req)
return nil, nil
}
为什么在 Handle 泛型函数中，proto.Unmarshal 不能将 'msg'（类型为 *T）用作 Message 类型？
如何在泛型函数中使用 new(T) 与 protobuf？
英文:
type Msg[T any] interface {
*T
proto.Message
}
func Handle[T any, U Msg[T]](cb func(req U) (proto.Message, error)) {
msg := new(T)
if err := proto.Unmarshal([]byte{}, msg); err != nil {
}
_, _ = cb(msg)
}
func main() {
Handle(donSomething)
}
func doSomething(req *pb.Hello) (proto.Message, error) {
_ = proto.Unmarshal([]byte{}, req)
return nil, nil
}
why proto.Unmarshal Cannot use 'msg' (type *T) as the type Message in Handle generic funcion.
how can i use new(T) in a generic funcion with protobuf
答案1
得分: 2
在你的程序中，T受到any的限制，所以指针类型*T与protobuf类型没有任何关系。它只是一个指向未指定类型的指针。
相反，使用以下方式：
msg := U(new(T))
这样，你就有了一个非nil的指针，指向被推断为pb.Hello的T类型。new(T)创建了一个指向pb.Hello零值的指针，而转换U()告诉编译器*T确实满足proto.Message接口。
英文:
In your program T is constrained by any, so the pointer type *T bears no relation to the protobuffer type anymore. It's just a pointer to an unspecified type.
Instead use:
msg := U(new(T))
This way you have a non-nil pointer to whatever T is inferred to — here it will be pb.Hello, new(T) creates a pointer to a pb.Hello zero value, and the conversion U() tells the compiler that *T really satisfies the proto.Message interface.
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