Virtual opBinary in interface

[sfp]

On Friday, 20 December 2024 at 18:40:17 UTC, Ali Çehreli wrote:
> On 12/19/24 10:49 AM, sfp wrote:
> > Subject lines says it all
>
> Although you clearly have a need for, virtual operators haven't 
> been common in my experience. I always felt they could cause 
> semantic issues.
>
> ...
>
> But it uses his magical implementation (enabled by D) of open 
> methods (and multi-methods).
>
> Ali

Right, the semantics can be a little odd, but there are 
definitely use cases for it which are very natural. Modeling how 
different kinds of animals mingle, I'm not sure... :-)

"Virtual binary operators" are quite useful in computational 
science (my field...). For instance, with a numerical linear 
algebra library, you might have sparse matrices, dense matrices, 
diagonal matrices, Toeplitz matrices, matrices which are only 
accessible indirectly via their action (e.g. you multiply with a 
discrete Fourier transform matrix by applying the FFT and do not 
store the matrix itself), *block* matrices (comprised of other 
matrices), etc, etc.

It is pretty common to mix and match these heterogeneously. 
MATLAB and Python have dense and sparse matrices, potentially 
other user-defined matrices/operators, and mixing and matching 
them is straightforward. Duck-typing is especially nice here, 
because there is no need to return a super type... multiply a 
dense matrix with a diagonal matrix and return a dense matrix 
(rather than a matrix supertype), no problem...

I actually saw this multimethod implementation in another forum 
post when searching around, but not the talk. Thanks for posting 
it. I will definitely take a look, but unless I'm mistaken, D 
doesn't have free binary operators?