[type_enthusiast]

A colleague (who is probably one of the smartest people I've met) made VectorFlow targeting D: https://github.com/Netflix/vectorflow

I've never had a chance to look at it much, but I think the magic is in the metaprogramming capabilities. It's more principled than C++ templates, more ergonomic than Scala macros, and more practical than Template Haskell. Somehow. (At least this was my impression from discussing it)

[riwsky]

The library looks impressive, but I dunno about that sales pitch: isn't "more principled than C++ templates"… a pretty low bar? And isn't "more practical than Template Haskell"… also a pretty low bar? I would have asked the same rhetorical question of Scala macros a couple years back, but the Scala 3 macro redesign is indeed pretty nice.

[WalterBright]

While the design D picked for templates looks (and is) straightforward, it wasn't obvious. It's only obvious in retrospect (which is something a good design aspires to, like putting an eraser on the other end of the pencil).

[riwsky]

I agree. That one can e.g. lift every binary operator at once with just a few lines of code makes even python overloading feel heavy—but readers can still understand it easily.

My point isn't that "D doesn't meet that bar", but that the GP picked strange points of comparison: the steelman argument for C++ templates would focus on power (e.g. Eigen) instead of principles, and those for Template Haskell on safety instead of practicality. And of course, no macro comparison would be complete without gesturing vaguely in the direction of Lisp while muttering something about parentheses.

It's like the "Always Be Closing" speech in Glengarry Glen Ross: Dlang macros as John Travolta truly do kick ass in that scene—but why not have Al Pacino there to represent as top dog of the local branch?