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.Responsetype
> EnrichedResponse generated.Response// Add a method that depends only on
> rfunc (r *EnrichedResponse) Enriched() int { return r.foo + 42}// Return
> the enriched responsefunc (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
>
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