Re: [go-nuts] Adding methods to non local types that use more state than available in the non local type

[Robert Engels]

If you look at the example given the function accepts the base type and then tries to call the function needing the extended type - pretty sure you can’t do this with embedding as the type is erased when the outer function is called. You need an interface afaik.  On May 11, 2025, at 8:43 PM, Jason E. Aten <j.e.a...@gmail.com> wrote: I think you have just misunderstood how to embed types in Go, because you say > // Declare a new type that embeds the generated.Response > type EnrichedResponse generated.Response and this is not type embedding, it is just a type definition, giving a new name and new type for the existing structure that is generated.Response. Here is an example of embedding: type EnrichedResponse struct {    generated.Response // notice there is no field name here, but in literals refer to it by generated.Response    otherNewState int } Now you can call any Reponse methods on EnrichedResponse, and also call new methods that you add to EntrichedResponse. On Monday, May 12, 2025 at 1:11:22 AM UTC+1 Robert Engels wrote: Just have the parameters be interfaces and do reflection/type casting.  On May 11, 2025, at 5:25 PM, Alexander Shopov <a...@kambanaria.org> wrote:  Hi all, I need some guidance whether what I want to do is somehow possible in Go. I've already searched answers for two days. My problem boils down to how to sneak more in a type without changing the type. Lets say I have to implement the following method: func (s *server) Get(ctx context.Context, request *generated.Request) (*generated.Response, error) {     var response generated.Request     return &response, nil } In this case it is a zero value (nil) that will be returned for response but that is not the problem - I am just marking the types I want to return a response that somehow implements a wider interface than generated.Response Since that object is generated source, I cannot change it or add methods to it, however I can do the following: // Declare a new type that embeds the generated.Response type EnrichedResponse generated.Response // Add a method that depends only on r func (r *EnrichedResponse) Enriched() int {     return r.foo + 42 } // Return the enriched response func (h *handler) Get(ctx context.Context, request *generated.Request) (*generated.Response, error) {     var enriched EnrichedResponse     response := generated.Response(enriched)     return &response, nil } My problem is the Enriched() method - it can only use the state available in the initial generated.Response and I need more in order to implement the functionality. I cannot just make EnrichedResponse a struct embedding generated.Response and add more state because then I cannot do the conversion from normal response to enriched. So here is my question - is there any way to have this state somewhere so that the Enriched() method does not take more arguments but can be called directly. A method declaration in Go is quite static. Additional state can be kept in some kind of closure but then I have no idea how to glue that closure to the method. Is there any trick I am missing? ----- Why would I want to do this? What am I trying to achieve? Basically there is a lot of generated code and I want to keep compatibility with it. Similar to the way Go embeds wider interfaces into narrower ones I want to be able to add methods to the generated code without having to change it. Then - whenever some code calls the Get method on the server - based on the whether the returned value implements the Enriched interface or not and the value it returns - I can dispatch behavior. Kind regards: al_shopov -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/bbe6bcd8-e33c-41bf-868a-e498561c3e72n%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/96f2f60e-61c6-4df3-984b-d14583013354n%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/75913DC6-E8EE-44A0-AD94-C3066E433379%40ix.netcom.com.