反射-方法调用恐慌，“调用struct value上的reflect.Value.Elem”

Question

Here is a code snippet -

type Gateway struct {
    Svc1 svc1.Interface
    Svc2 svc2.Interface
}

func (g *Gateway) GetClient(service string) interface{} {
    ps := reflect.ValueOf(g)
    s := ps.Elem()
    f := s.FieldByName(strings.Title(service))
    return f.Interface()
}

func (g *Gateway) Invoke(service string, endpoint string, args... 
    interface{}) []reflect.Value {
    log.Info("Gateway.Invoke " + service + "." + endpoint)
    inputs := make([]reflect.Value, len(args))
    for i, _ := range args {
        inputs[i] = reflect.ValueOf(args[i])
    }

    client := g.GetClient(service)

    return reflect.ValueOf(client).Elem().MethodByName(endpoint).Call(inputs)
}

GetClient("svc1") works fine.

However, when I call Invoke("svc1", "endpoint1", someArg), it panics saying -

reflect: call of reflect.Value.Elem on struct Value

reflect.ValueOf(client).MethodByName(endpoint).Call(inputs) panics saying Call on a zero value.

Answer 1

There are a couple issues:

1. If svc1.Interface is not a pointer or an interface, reflect.Value.Elem() will panic (see https://golang.org/pkg/reflect/#Value.Elem)

2. If the endpoint argument string of Invoke doesn't match the capitalization of the target method, it will panic due to zero value (invalid reflect.Value). Please note that the method you want to call must be exported.