Why can't I inherit (extend) structs?

[Lionello Lunesu]

"Mike Parker" <aldacron71 at yahoo.com> wrote in message 
news:eggji8$1kih$1 at digitaldaemon.com...
> Lionello Lunesu wrote:
>> I like the definition of 'struct' in D: simple aggregations of data. But 
>> is there currently a way to extend a struct? Apart from composition, that 
>> is. I'd like to do something like this:
>>
>> struct X {
>>   int x;
>> }
>>     struct Z : X {
>>   int z;
>> }
>>
>> Would this feature add complications that I fail to see?
>>
>> It's not a big deal, since I can use composition, but I'll have to name a 
>> member for the first struct and repeatedly write it.. And I'm lazy :S
>>
>
> Once you start extending structs, you'll need the same bookkeeping 
> overhead required for classes. That eliminates the current distinction 
> between them.

I don't need polymorphism and all that, just to add fields to an existing 
struct, like Derek's example: struct ColorRGB and then a struct ColorRGBA, 
which adds a field for the alpha (=transparency). Seems I can use mixins for 
this, at the moment.

But there's shouldn't be extra bookkeeping. It should be like composition; 
like adding a nameless instance of the 'base' struct as the first member in 
the derived struct.

L.