True value semantics for class or struct?

[Ali Çehreli]

On 11/29/2012 06:25 PM, js.mdnq wrote:
> Simple values are ones that act atomically and use the standard
> mathematical operations.
>
> Suppose I would like to wrap an int with additional functionality:
>
> struct SmartInt{
> privatedata
> int Value;
> methods
> }
>
> The idea is that SmartInt semantics are treated identical to SmartInt.Value
>
> So SmartInt = 3; is identical to SmartInt.Value = 3;
>
> But since it is a smart int we can do
>
> SmartInt.SomeMethod()
>
> Also, when a the struct is copied I might not want to copy privatedata
> as it might change the functionality(maybe instead of copying I want it
> to be set to 0, through a constructor, or method).
>
> The main purpose though, is to treat SmartInt and SmartInt as one and
> the same semantically. As far as I'm concerned, SmartInt is an int... I
> just "wrapped" it up with some nice functions.
>
> Is anything like this possible in D?
>
>
>

There is 'alias this':

struct SmartInt{
     int Value;
     double privatedata;
     void someMethod()
     {}

     alias Value this;

     /* Note: A more intuitive syntax is coming with dmd 2.061:
      *
      *  alias this = Value;
      *
      * (I hope I remembered it correctly. :p)
      */
}

void main()
{
     auto s = SmartInt(42);
     s = 45;
     int result = s + 43;
     s.someMethod();
}

Ali