New library: open multi-methods

[James Dean via Digitalmars-d-announce]

On Sunday, 16 July 2017 at 17:24:17 UTC, Jean-Louis Leroy wrote:
> Hello,
>
> TL;DR: see here 
> https://github.com/jll63/methods.d/blob/master/README.md for an 
> explanation of what open multi-methods are, if you are not 
> familiar with the idea.You may also want to read my article on 
> Code Project 
> https://www.codeproject.com/Articles/635264/Open-Multi-Methods-for-Cplusplus11-Part-1
>
> Earlier this year I attended Ali Çehreli's talk at C++ Now. He 
> did a good job: I walked out with the desire to learn about D 
> and see how it measures up against C++, especially in terms of 
> meta-programming and language extensibility. The first 
> programming language I learned is Forth and I did some Lisp 
> programming, so as you can imagine, my expectations are high.
>
> As an experiment, I decided to try to port parts of my yomm11 
> library to D. The experience turned out to be pleasant and I 
> ended up writing a full implementation, with some friendly help 
> from Ali and others in the Learn forum.
>
> I think that what I have now is good enough to show. The git 
> repo is here https://github.com/jll63/methods.d and I will post 
> a package to the registry soon.
>
> If you have the inclination, feel free to review and comment. 
> This is my very first D project and I certainly have missed 
> some idioms and been clumsy at times.
>
> Jean-Louis Leroy

Interesting. One problem I think the above approach has is adding 
methods after compilation. Say, a plugin adds a new derived 
matrix type SparseMatrix and wants to customize the addition of 
them. This is impossible under the current model, is it not?

Would it not be possible create a sort of "externmultimethod" 
that mimics extern'ing a method? Basically, on the "server/host" 
side there is a method that can be used to add new multimethods 
at runtime. It takes meta data and extends the virtual table to 
handle dispatching it along with the other functions. The 
"client/plugin" side has the multimethod it wants to add to the 
dispatch and it does this by giving it all the needed information 
to do so and using the new externmultimethod method to do it.