Templated Interfaces?

[Jason House]

Simen Kjaeraas wrote:

> On Sun, 24 Aug 2008 22:20:46 +0200, Benji Smith <dlanguage at benjismith.net>
> wrote:
> 
>> Ary Borenszweig wrote:
>>> Benji Smith a écrit :
>>>> I've been trying to create a templated interface, and can't figure out
>>>> what I'm doing wrong. Here's the basic example:
>>>>
>>>> interface I(T) {
>>>>   public T x();
>>>> }
>>>>
>>>> class C(T) : I(T) {
>>>  class C(T) : I!(T) {
>>
>> Very nice! Thanks!
>>
>> Now let's say I want to create an array of those interface instances:
>>
>> interface I(T) {
>>    public T x();
>> }
>>
>> class C(T) : I!(T) {
>>    private T value;
>>    public this(T val) { this.value = val; }
>>    public T x() { return value; }
>> }
>>
>> void main() {
>>    I!(char)[] array = new I!(char)[];
>>    array ~ new C!(char)('a');
>>    array ~ new C!(char)('b');
>>    array ~ new C!(char)('c');
>>    char value = array[0].x();
>> }
>>
>> Now the compiler is complaining about the line where I create the array.
>> It says "Error: new can only create structs, dynamic arrays or class
>> objects, not I[]'s"
>>
>> Obviously, I'm trying to create a dynamic array of interface instances,
>> so I'm not sure what I'm doing wrong.
>>
>> Thanks!
>>
>> --benji
> 
> You do not need to initialize the the array with the "new I!(char)[]".
> Just use
> 
> I!(char)[] array;
> array ~= new C!(char)('a');
> ...
> char value = array[0].x();
> 

whoa, that's a bad idea!

You can not implicitly cast back and forth between interfaces and classes
that implement those interfaces; the underlying pointer is not the same. 
There was a big discussion about this fairly recently on one of the D
mailing lists...