Re: 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