How to avoid repeating myself in Go? - go

Question

I just started with Go, and my background includes generics. Since Go still does not support generics, I'm wondering how do I keep my code DRY?
Take a look at the example below, the request argument has a dynamic type, which returns a dynamic response (PaymentMethodResponse). If I want to create another request, I copy and paste the whole code inside the method, changing only the type of the request and response and the localVarPath variable.
/*
PaymentMethods Returns available payment methods.
Queries the available payment methods for a transaction based on the transaction context (like amount, country, and currency). Besides giving back a list of the available payment methods, the response also returns which input details you need to collect from the shopper (to be submitted to `/payments`). Although we highly recommend using this endpoint to ensure you are always offering the most up-to-date list of payment methods, its usage is optional. You can, for example, also cache the `/paymentMethods` response and update it once a week.
* #param request PaymentMethodsRequest - reference of PaymentMethodsRequest).
* #param ctxs ..._context.Context - optional, for authentication, logging, cancellation, deadlines, tracing, etc. Passed from http.Request or context.Background().
#return PaymentMethodsResponse
*/
func (a *Checkout) PaymentMethods(request *PaymentMethodsRequest, ctxs ..._context.Context) (PaymentMethodsResponse, *_nethttp.Response, error) {
var (
localVarHTTPMethod = _nethttp.MethodPost
localVarPostBody interface{}
localVarReturnValue PaymentMethodsResponse
)
// create path and map variables
localVarPath := a.BasePath() + "/paymentMethods"
localVarHeaderParams := make(map[string]string)
localVarQueryParams := _neturl.Values{}
// to determine the Content-Type header
localVarHTTPContentTypes := []string{"application/json"}
// set Content-Type header
localVarHTTPContentType := common.SelectHeaderContentType(localVarHTTPContentTypes)
if localVarHTTPContentType != "" {
localVarHeaderParams["Content-Type"] = localVarHTTPContentType
}
// to determine the Accept header
localVarHTTPHeaderAccepts := []string{"application/json"}
// set Accept header
localVarHTTPHeaderAccept := common.SelectHeaderAccept(localVarHTTPHeaderAccepts)
if localVarHTTPHeaderAccept != "" {
localVarHeaderParams["Accept"] = localVarHTTPHeaderAccept
}
// body params
if request != nil {
localVarPostBody = request
}
var ctx _context.Context
if len(ctxs) == 1 {
ctx = ctxs[0]
}
r, err := a.Client.PrepareRequest(ctx, localVarPath, localVarHTTPMethod, localVarPostBody, localVarHeaderParams, localVarQueryParams)
if err != nil {
return localVarReturnValue, nil, err
}
localVarHTTPResponse, err := a.Client.CallAPI(r)
if err != nil || localVarHTTPResponse == nil {
return localVarReturnValue, localVarHTTPResponse, err
}
localVarBody, err := _ioutil.ReadAll(localVarHTTPResponse.Body)
localVarHTTPResponse.Body.Close()
if err != nil {
return localVarReturnValue, localVarHTTPResponse, err
}
if localVarHTTPResponse.StatusCode >= 300 {
newErr := common.NewAPIError(localVarBody, localVarHTTPResponse.Status)
return localVarReturnValue, localVarHTTPResponse, newErr
}
err = a.Client.Decode(&localVarReturnValue, localVarBody, localVarHTTPResponse.Header.Get("Content-Type"))
if err != nil {
newErr := common.NewAPIError(localVarBody, err.Error())
return localVarReturnValue, localVarHTTPResponse, newErr
}
return localVarReturnValue, localVarHTTPResponse, nil
}
Example of usage: (request is a json struct)
res, httpRes, err := client.Checkout.PaymentMethods(&checkout.PaymentMethodsRequest{})

Answer 1

You can use the same approach as the one used by json.Unmarshal and other decoders/unmarshalers that accept an argument of type interface{} and instead of returning a value of an unknown type they store the result of their operation into the provided interface{} argument.
Here's example pseudo code:
func apicall(req, res interface{}) error {
inputbody, err := jsonencode(req)
if err != nil {
return err
}
response, err := httpclient.postrequest(inputbody)
if err != nil {
return err
}
return jsondecode(res, response.body)
}
func main() {
req := new(PaymentMethodsRequest)
res := new(PaymentMethodsResponse)
if err := apicall(req, res); err != nil {
return err
}
// do something with res
}