@Alex,
Oh, and I should point out that I actually went with what you mentioned in
your 1st point, I was just curious if it was possible to do it the other
way.
On Saturday 30 December 2023 at 20:36:07 UTC+1 Mazen Harake wrote:
> Cheers @Axel for the input. I think I worked it out though.
>
> The bad thing is that it involves reflection but considering that it
> greatly simplifies the code base I would argue that it is good enough for
> now.
>
> First, regarding your 2nd point of passing buf as a parameter to Decode()
> instead of through a field. The examples I gave are made up to resemble the
> actual situation to simplify it but what actually happens is that each
> message has a "BaseMessage" struct. When receiving some payload the common
> parts of the message (such as the length, type and checksums) are always
> decoded into base message, then depending on the type the specific message
> type is created and the rest of the bytes are decoded according to what
> that message expects.
>
> Anyway... this is the solution I came up with (for internet searching
> completeness sake):
>
> func DecodeMessage[T Decoder](bm *BaseMessage) (T, bool) {
> var mT T
> m := reflect.New(reflect.TypeOf(mT).Elem()).Interface().(T)
> d := Decoder(m)
> ok := d.Decode( bm )
> return d.(T), ok
> }
>
> This function is then called with the following code example:
>
> transactionMsg, ok := DecodeMessage [*TransactionMessage](baseMsg)
>
> Cheers
>
>
> On Friday 29 December 2023 at 23:17:47 UTC+1 Axel Wagner wrote:
>
> 1. Note that you can just write `NewMessage(&MessageA{}, buf)` in your
> example, as the type can be inferred.
> 2. You can use a constraint on a pointer-receiver to somewhat simplify
> that: https://go.dev/play/p/pEu02Bn9t3f
> That is not *quite* what you are asking for. It is not actually possible
> to really do what you want, because there is no way to express a constraint
> that "the type needs to have a `Buf []byte` field, which would be needed to
> make your `m := &MessageAStruct{Buf: b}` work. But there isn't really a
> reason to pass the buffer as a field anyways, in my opinion - passing it as
> a parameter to `Decode` seems far more logical.
>
> On Fri, Dec 29, 2023 at 8:52 PM Mazen Harake <[email protected]> wrote:
>
> Hi all,
>
> Assume I have a tcp server with incoming tcp packets which can be decoded
> in differently depending on some headers in that packet.
>
> Each message that comes in has a struct associated with it which can be
> created with the traditionale NewX..(buf []byte ...). After creating the
> object (or inside the constructor, doesn't matter) the Decode() function is
> called to interpret the bytes and assign all the fields of the struct.
>
> This works fine. But is it possible to eliminate all the 200+ functions
> that do the same thing but use a generic function instead?
>
> So instead of this:
>
> func NewMessageA(buf []byte) *MessageAStruct {
> m := &MessageAStruct{
> Buf: buf,
> }
> m.Decode()
> return m
> }
>
> msg := NewMessageA(buf)
>
> I would rather do something like this:
>
> msg := NewMessage[A](buf)
>
> and I would've wanted to do something like this in the generic function
>
> func NewMessage[T](buf []byte) *T {
> // ... something?
> // call Decode()
> // return *T
> }
>
> I can do it by creating an interface called Decodable and then passing the
> the type and the "empty" object to the generic function but it feels clumsy
> and weird somehow and I probably wouldn't gain very much. E.g.
>
> func NewMessage[T Decodable](t T, buf []byte) T {
> t.Decode(buf)
> return t
> }
>
> and I would call it like this
>
> msg := NewMessage[*MessageA](&MessageA{}, buf)
>
> The most likely answer is "You shouldn't do it like that", which would be
> a completely fine and acceptable answer, but *can* you achieve this?
>
> Cheers
>
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