Handle to some object, call its methods

[Anonymous via Digitalmars-d-learn]

On Tuesday, 15 July 2014 at 17:06:14 UTC, Ali Çehreli wrote:
> On 07/15/2014 09:39 AM, Anonymous wrote:
>
> > struct Subscription {
> >      const Object handle;
> >      private immutable size_t index;
> >      @disable this();
> >      private this(Object o, size_t i) {
> >          handle = o;
> >          index = i;
> >      }
> > }
> >
> > I'd like this to be constructed with a handle to some object,
> and some
> > other details. The source would create and return the
> Subscriptions, and
> > the reader would call the object's const methods through the
> handle. The
> > const "read" methods would take the Subscription as one of
> the arguments.
>
> Object is too general for that. Normally, you would define an 
> interface and use that:
>
> interface Reader
> {
>     int read() const;
> }
>
> struct Subscription {
>      const Reader reader;
>      private immutable size_t index;
>      @disable this();
>      private this(Reader r, size_t i) {
>          reader = r;
>          index = i;
>      }
> }
>
> class ConstantReader(int value) : Reader
> {
>     int read() const
>     {
>         return value;
>     }
> }
>
> void main()
> {
>     auto sub = Subscription(new ConstantReader!42(), 0);
>     assert(sub.reader.read() == 42);
> }
>
> Further, if 'index' is the subscription index, usually there is 
> no need for that as the Subscription objects can be iterated 
> over in their container:
>
>     Subscription[] subs;
>     subs ~= Subscription(new ConstantReader!42(), 0);
>
>     foreach (sub; subs) {
>         sub.reader.read();
>     }
>
> Ali

Thanks, that adapted well.