[Ns-developers] [ns3] trace path documentation

[Gustavo Carneiro]

On 14/04/2008, Mathieu Lacage <mathieu.lacage at sophia.inria.fr> wrote:
>
>
> On Fri, 2008-04-11 at 01:28 +0100, Gustavo Carneiro wrote:
>
>
>
> >         There are a couple of issues to consider:
> >           - I had to make one API change to the attribute system: if
> >         you want to
> >         set or get a pointer of the form Ptr<T> as an attribute, you
> >         must now
> >         wrap that pointer in an instance of the Pointer class.
> >         Ptr<Queue> queue;
> >         queue = csma->GetAttribute ("TxQueue");
> >         is now:
> >         Ptr<Queue> queue;
> >         Pointer q = csma->GetAttribute ("TxQueue");
> >         queue = q.Get ();
> >
> > Ugh!..
> >
> > Can you at least rename it to PointerAttribute or something.  Having
> > both Pointer and Ptr is rather confusing.
> >
> > Moreover, generally I think all classes that only wrap attribute
> > values and which have a Get() method should be renamed to FooAttribute
> > (replace Attribute with a suffix of choice).  That would make it clear
> > when a class is only a wrapper to an actual value.
>
>
> Thinking more about this and other issues lead me to re-consider this
> problem in light of the larger problem of trying to explain in a
> sensible and consistent way how to set and get attributes in objects or
> across the helper API. The issue we face in the current code and in what
> you propose is that different attributes get a different treatment
> because of implementation details (which make a lot of sense if you know
> how the implementation works but which are pretty weird for a user). For
> example, if I want to deal with a double:
>
> object->SetAttribute ("MyDouble", Double (10.0));
> Double v = object->GetAttribute ("MyDouble");
> double value = v.Get ();
>
> but, if I want to deal with a Vector:
>
> Vector v = Vector (0.0, 0.0, 0.0);
> object->SetAttribute ("MyVector", vector);
> v = Object->GetAttribute ("MyVector");
>
> The issue, here, is that you have to wrap the value you want to set or
> get with a Double but not with a Vector.
>
> The only way to make the two classes of attributes behave the same is to
> _always_ request that you use a 'wrapper' class to set or get an
> attribute:
>
> object->SetAttribute ("MyDouble", DoubleAttribute (10.0));
> object->SetAttribute ("MyVector", VectorAttribute (v));
> DoubleAttribute v = object->GetAttribute ("MyDouble");
> double doubleV = v.Get ();
> VectorAttribute vec = object->GetAttribute ("MyVector);
> Vector vectorV = vec.Get ();
>
> The above code is certainly verbose but it is at least very consistent
> and avoids the problem you originally complained about. Would there be
> complaints if I implemented that ?


No objections from me, but maybe DoubleAttr is good enough name and shorter
to type?...

regards,
>
> Mathieu
>
>
>


-- 
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert