Multiple alias this, what's the hold up?

[Mike Franklin]

On Sunday, 16 June 2019 at 22:28:56 UTC, Walter Bright wrote:

>> I refer you to this StackOverflow question 
>> (https://stackoverflow.com/questions/255553/is-it-possible-to-implement-mixins-in-c) where a C# user was looking for a convenient way to reuse and aggregate implementations.  The second comment to the question says it all:
>> 
>>> I find it annoying that C++ experts make statements like 
>>> "Prefer composition to inheritance" yet the language (C++ or 
>>> C#) offers precious little help to do the "right thing".
>
> Be careful about dismissing what experts say. Sometimes it 
> takes many years of experience to understand that seemingly 
> good ideas are not that good after all.
>
> I don't do use a lot of programming techniques I thought were 
> way cool in my 20's, but now I understand are crap, like <cough 
> cough>macros</cough cough>.

I think you may have misunderstood what that user and I are 
saying.  We're not dismissing what the experts say, in fact we, 
for the most part, agree with them.  What we're saying is that 
the facilities for composition in C# and C++ are lacking, yet 
those experts, disingenuously, aren't acknowledging it.

D has an opportunity, and is better positioned, to do better.  If 
C++ style multiple inheritances is not the answer, what is?  
Eiffel's multiple inheritance?  D's `alias this`? 
Design-by-introspection metaprogramming? "Suck it up, and get 
typing!"?

Mike