I am slightly confused. As an exercise, I am writing a simple 3D vector class. Part of this involves playing with operator overloading. Here's some of the class:

class Vector3D {
public:
    real x, y, z;

    this(real x, real y, real z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }
    this() { this(0, 0, 0); }

    Vector3D opAdd(Vector3D r) {
        return new Vector3D(x + r.x, y + r.y, z + r.z);
    }
}

This was my first stab at the opAdd function, and I think it looks most right. In poking around dsource, I have also seen such functions written like:

    Vector3D opAdd(Vector3D r) {
        Vector3D v;
        v.x = x + r.x;
        v.y = y + r.y;
        v.z = z + r.z;
        return v;
    }

(The example I'm thinking of is seen here:
http://www.dsource.org/projects/tutorials/wiki/CurrencyExample
)

So, where's v here? Is D implicitly doing "new Vector3D()"? Is this better, worse, or not different compared to what I did? Where is this mentioned in the spec? (I couldn't find it.)

-Kirk McDonald

Kirk McDonald wrote:

> I am slightly confused. As an exercise, I am writing a simple 3D vector class. Part of this involves playing with operator overloading. Here's some of the class:
> 
> class Vector3D {
> public:
>      real x, y, z;
> 
>      this(real x, real y, real z) {
>          this.x = x;
>          this.y = y;
>          this.z = z;
>      }
>      this() { this(0, 0, 0); }
> 
>      Vector3D opAdd(Vector3D r) {
>          return new Vector3D(x + r.x, y + r.y, z + r.z);
>      }
> }
> 
> This was my first stab at the opAdd function, and I think it looks most right. In poking around dsource, I have also seen such functions written like:
> 
>      Vector3D opAdd(Vector3D r) {
>          Vector3D v;
>          v.x = x + r.x;
>          v.y = y + r.y;
>          v.z = z + r.z;
>          return v;
>      }
> 
> (The example I'm thinking of is seen here: http://www.dsource.org/projects/tutorials/wiki/CurrencyExample )
> 
> So, where's v here? Is D implicitly doing "new Vector3D()"? Is this
> better, worse, or not different compared to what I did? Where is this
> mentioned in the spec? (I couldn't find it.)

In the latter case, Vector3D seems to be a struct rather than a class, and as such, it is passed by value and not created with new. See more about the different semantics of structs and classes in D in the docs.

/Oskar

Kirk McDonald wrote:
> I am slightly confused. As an exercise, I am writing a simple 3D vector class. Part of this involves playing with operator overloading. Here's some of the class:
> 
> class Vector3D {
> public:
>     real x, y, z;
> 
>     this(real x, real y, real z) {
>         this.x = x;
>         this.y = y;
>         this.z = z;
>     }
>     this() { this(0, 0, 0); }
> 
>     Vector3D opAdd(Vector3D r) {
>         return new Vector3D(x + r.x, y + r.y, z + r.z);
>     }
> }
> 
> This was my first stab at the opAdd function, and I think it looks most right. In poking around dsource, I have also seen such functions written like:
> 
>     Vector3D opAdd(Vector3D r) {
>         Vector3D v;
>         v.x = x + r.x;
>         v.y = y + r.y;
>         v.z = z + r.z;
>         return v;
>     }
> 
> (The example I'm thinking of is seen here:
> http://www.dsource.org/projects/tutorials/wiki/CurrencyExample
> )
> 
> So, where's v here? Is D implicitly doing "new Vector3D()"? Is this better, worse, or not different compared to what I did? Where is this mentioned in the spec? (I couldn't find it.)
> 
> -Kirk McDonald


This only works with sturcts. As Oskar said, structs don't need to be newed, they are by value.

Now that I look at http://www.dsource.org/projects/tutorials/wiki/CurrencyExample
I see that it's doing it on a class! The code must be borken.

Hasan Aljudy wrote:
> Now that I look at http://www.dsource.org/projects/tutorials/wiki/CurrencyExample I see that it's doing it on a class! The code must be borken.
> 

You'll also notice that the opAdd method in that example takes two arguments instead of one.

Apparently, since the method's never called in the code (it might as well be removed) the error hasn't been noticed.

Hasan Aljudy wrote:
> This only works with sturcts. As Oskar said, structs don't need to be newed, they are by value.
> 
> Now that I look at http://www.dsource.org/projects/tutorials/wiki/CurrencyExample
> I see that it's doing it on a class! The code must be borken.
> 

Ah! That would do it. So the way I did it first is the proper way?

-Kirk McDonald

"Kirk McDonald" <kirklin.mcdonald@gmail.com> wrote in message

> Ah! That would do it. So the way I did it first is the proper way?

Yes, that's the right way to do it for classes.