Re: Clay language

[Steven Schveighoffer]

On Thu, 30 Dec 2010 21:14:28 -0500, Simen kjaeraas  
<simen.kja...@gmail.com> wrote:

Andrej Mitrovic <andrej.mitrov...@gmail.com> wrote:
On 12/31/10, Simen kjaeraas <simen.kja...@gmail.com> wrote:


This will give you both:

class A
{
    void bar(this T) ( )
    {
        writeln(typeid(T));
        writeln(typeid(this));
    }
}

class B : A
{
}

void main( )
{
    A a = new B;
    a.bar();
}

Indeed it will. Now, if you look closely, you will see that typeid(T) is  
A, while typeid(this) is B. Testing further:

class A {
    void baz() {
        writeln(typeid(this));
    }
}
class B : A {
}

void main() {
     A a = new B;
     a.baz(); // prints B.
}

We thus see that the template this parameter has absolutely no value.

No, it does have value:

class A
{
   string x;
   T setX(this T, U)(U newx)
   {
      this.x = to!string(newx);
      return cast(T)this;
   }
}

class B : A
{
   int y;
   void setY(int newy)
   {
      this.y = newy;
   }
}


void main()
{
   auto b = new B;
   b.setX(5).setY(6);
}

Hey, look! covariance with templates :)

Now if only templates worked in interfaces...

I also have to write a helper function to eliminate that cast (which does  
a runtime lookup).

-Steve