Re: Ada Distilled by Richard Riehle

["Dan'l Miller" <optikos@verizon.net>]

On Friday, July 27, 2018 at 4:32:52 PM UTC-5, Dmitry A. Kazakov wrote:
> On 2018-07-27 22:38, Dan'l Miller wrote:
> > On Friday, July 27, 2018 at 3:07:21 PM UTC-5, Dmitry A. Kazakov wrote:
> >> - full MD
> > 
> > Full multiple dispatch was added experimentally back in the day for Ada as part of the Ada9X exploratory contracts, by SRI iIRC.
> 
> MD is a difficult problem with regard to separate compilation. I don't 
> know how to solve it in a consistent way.
> 
> But the language design goal should be that any operation declared 
> publicly must have all arguments and results controlling or class-wide. 
> No contravariance. No type-specific operations.

http://www.stroustrup.com/multimethods.pdf
Above is an interesting research report (and survey of the 2007 then-state of the art) from C++world on this topic of how to efficiently implement openmultimethods.  (Ada95 fortunately chose a variant of open methods for the syntax of single-dispatch, which should extend quite nicely to openmultimethod syntax, whereas C++ with openmultimethod feature would need to graft on a foreign-language-feeling Ada95-esque syntax.)

Cutting to the chase scene:
A) they seem to drop breadcrumbs per compilation-unit that are then stitched together  in the linker to then author the (dense?) multidimensional array in one fell swoop,
instead of
B) each compilation-unit contributing its portion fully-formed in situ in the one multidimensional dispatch array.

I am not understanding how the Chinese-remaindering alternative design is better in •any• metric at all (e.g., smaller memory footprint? but why the N/A in the table in §7.2?), unless their multidimensional dispatch array was sparse (for no good reason) instead of dense.