英文:
golang protobuf can not unmarshal in a generic type
问题
proto.Unmarshal([]byte{}, req)
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，因此指针类型 *T 不再与 protobuffer 类型相关。它只是一个指向未指定类型的指针。
而应该使用：
msg := U(new(T))
这样，你就会得到一个非空指针，指向推断出的 T 的类型 — 在这里它将是 pb.Hello，new(T) 创建一个指向 pb.Hello 零值的指针，而转换 U() 告诉编译器 *T 真正满足 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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