How to get an actual instance out of a Go/Golang reflect.Value

invoke_method.go

//Author Geoffrrey Hendrey
//Here we dynamically invoke a method, passing the method the input, whose type we don't know. We know the method returns two things, a value and an errror. 
//(multiple return values). This code shows how we grab the error, which
//is the second return value of the method, check it it is not nil, and if not nil type-assert it to an actual error (line 11). They key is
//on line 11 where we extract the interface() from the errReflect, which is reflect.Value. Once we have an interface{} we can do the type-assertion.


func invokeMethod(method reflect.Value, input interface{}) (resp interface{}, err error) {
	in := []reflect.Value{reflect.ValueOf(input)}
	returnValuesFromClientCall := method.Call(in)
	errReflect := returnValuesFromClientCall[1] //this is the error return value from the call above
	if !errReflect.IsNil() {                    //if there was an error
		ifc := errReflect.Interface()
		err := ifc.(error)
		log.Errorf("method call returned error: %s", err.Error())
		return nil, err
	}
	return returnValuesFromClientCall[0].Interface(), nil
}