grep

[Dee Girl]

torhu Wrote:

> janderson wrote:
> > I guess your not being serious but in case you are, you want to make bad 
> > coding difficult to do and good coding easy.  People area not likely to 
> > go to that much effort to circumvent cast.  There are a couple of other 
> > ways to get around cast:
> > 
> > //ie
> > class A
> > {
> > 
> > };
> > 
> > class B : A
> > {
> > 
> > };
> > 
> > 	B[] b;
> > 	b ~= new B;
> > 	A[] a = b;
> > 	a ~= new A;
> > //b[1] Is not an A type (not a B type), but is essentially a reinterpret 
> > A -> B.
> > 
> 
> But array b has no element at index 1, it's length is still 1.
> 
> This gets the desired effect:
> 
>   	B[] b;
>   	b ~= new B;
>   	b ~= new B;
>   	A[] a = b[0..1];
>   	a ~= new A;
> 
> Now, the second element of b will be an A.  On the other hand, appending 
> to slices could easily be considered bad style.

I do not understand D arrays yet to know why appending to slices is bad style. But there is no need for slices. The following program compiles and runs. D makes a textbook mistake by making arrays covariant. Why nobody gets arrays right?

import std.stdio;

class A {}
class B : A {}

void main()
{
    B[] b = new B[2];
    A[] a = b;
    a[0] = new A;
    a[1] = new B;
    writeln(b[0]);
}

It is correct to allow B[] to be a subclass of const(A[]), but B[] can not be a subclass of A[] because elements of A[] can be written to and end up in the B[] array. Could D2 repair this bug? Dee Girl