根据运行时类型重载或避免if-else / switch-case

Question

My case is simple, I want to "map" exceptions to a HttpStatusCode. I could easily do this:

if (e is AuthenticationException)
{
    return HttpStatusCode.Forbidden;
}
else
{
    return HttpStatusCode.InternalServerError;
}

I would then add more else-if blocks checking the types.

Is there a better way of doing this? I can't use overloads, because the compile-time type of e is Exception , even though the runtime type will be something else. So this won't work (basic .NET OO):

private static HttpStatusCode GetHttpStatusCode(Exception e)
{
    return HttpStatusCode.InternalServerError;
}

private static HttpStatusCode GetHttpStatusCode(AuthenticationException e)
{
    return HttpStatusCode.Forbidden;
}

What would be an elegant way of coding this?

Answer 1

Well, maybe you can add a few catch in your code, for example:

try{
    //code here
}
catch(AuthenticationException e){
    return HttpStatusCode.Forbidden;
}
catch(InvalidOperationException e){
    return HttpStatusCode.InternalServerError;
}
catch(Exception e){
    return HttpStatusCode.InternalServerError;
}        

And another exceptions that you need in your code.

Answer 2

I'd create a Dictionary<Type, HttpStatusCode> for the mapping:

var dict = new Dictionary<Type, HttpStatusCode>
{
    { typeof(AuthenticationException), HttpStatusCode.Forbidden },
    // etc.
}

HttpStatusCode GetStatusCodeFromException(Exception e)
{
    HttpStatusCode code;
    if (!dict.TryGetValue(e.GetType(), out code))
        code = // Whatever default value you want
    return code;
}