Why can't structs be derived from?

[Ary Manzana]

On 3/15/11 4:06 PM, Steven Schveighoffer wrote:
> On Tue, 15 Mar 2011 14:54:13 -0400, Jens <jne at somewhere.org> wrote:
>
>> I didn't ask how to do composition in D. I asked why composition cannot
>> be done via derivation, i.e., the reasoning behind the language design
>> choice. A design faux paus IMO.
>
> Because composition by inheritance can be *completely* implemented using
> alias this -- a feature that also provides other niceties. Why provide
> another mechanism to do the exact same thing, just because you are used
> to it?
>
> Note that "inheritance" is actually done exactly this way in C++, by
> putting the derived type at the front of the "derived" type, and
> aliasing all the methods/fields into the derived namespace.
>
> Show me what composition by derivation provides that alias this does not.
>
> -Steve

Oh, come on, why use alias this when you can implement it in assembler?