Proof of concept for v2 - NO duplication, NO `static if` hell, NO difficulty with interoperability

[zjh]

>> Alexandrescu wrote:

`C++20` is very powerful, `d` can't be complacent. We should 
learn the advantages of `C++`. We should also  introduce powerful 
features such as `... `and `concept` and `coroutine` etc. What a 
convenient tool. Why not learn it?
Like `manu` made a proposal, why doesn't `Walter` accept it?
As a long history language, C++ is undergoing radical 
improvement, so should we. Just provide a transition period of 
about `5~6` years.
And `C++23` reflection library, is coming.