Hacker News Reader

Comment by nikki93 | Hacker News Reader

Can you eg. generate a struct with fields based on an existing struct or on a comptime array in D? Can you receive a structure literal of anonymous type and iterate over it at compile time? (curious bc. these were a few things I found straightforward in Zig, and in C++ the main proposals involve tons of new metaclasses and reflection features for)

View on HN

Yes to all points.

D doesn't go the C++ route, the way code like this works is via generating new code (in text) at compile time which the compiler then compiles (duh) and replaces the mixin statement within.

Here's an annotated example of these features in use

https://run.dlang.io/is/2b5zgC

Brilliant.

That is beautiful. I wish C++ had something like that... Perhaps in addition to its current template system. Having a separate build pass to generate files is annoying.

It does, via constexpr, which just got more expressive in C++20, and is the basis for the ongoing compile time reflection work on C++23.

Code injection might eventually come later via Microsoft's ongoing research in C++ metaclasses.

"Dynamic Polymorphism with Metaclasses and Code Injection"

https://www.youtube.com/watch?v=8c6BAQcYF_E

That looks a lot more complicated than D's simple "output text that gets fed back into the compiler". But admittedly I only quickly jumped around the video. Hopefully it works well, though.

True, but a programming language is more than just syntax and for better or worse, the ecosystem is what matters.

That's what I meant by doesn't go the C++ way. The standards committee over complicate everything (concepts still haven't landed yet for example, D has D a better more flexible system 15 years ago I think)

And no ecosystem to speak off, while that standards committee is making sure that GPGPU programming is the next killer application for C++.

How are modules coming along then?

C++ has succeeded despite the committee not because of it.

Already available as experimental on VC++, and approved as part of C++20.

As proven by every failed attempt to replace languages with industry standards, plenty of companies do care about ISO and ECMA language standards.

D is a nice language, but spends too much time focusing on the language and its cool metaprograming capabilities, without focus on the ecosystem.

Slowly Java, C#, C++ will have the features that made D unique, with the plus side of 20 - 40 years of libraries, IDE support and industry certifications.

Cool! Nim is related here, where instead of text manipulation you're doing AST manipulation with quasi-quoting (like in many lisps), eg. https://nim-lang.org/docs/tut3.html#introduction-building-yo....

Reply on news.ycombinator.com