C++ became more and more cryptic. Make C++ code creation programmable (templating) by basic c++ syntax at compile time. Make this a part of the standard library.
jandrewrogers · 1h ago
I am looking forward to compile-time reflection, C++ has unusually strong metaprogramming capabilities among systems languages and this will significantly bolster that.
C++ does not win any prizes for being the most aesthetically pleasing programming language but the new syntax around reflection is pretty ugly even by those standards.
npalli · 1h ago
Also, it is worthwhile reading the standard proposal paper for lot of examples of how this might be used in the future.
The rationale in section 2.2 for the single std::meta::info type is interesting. While having a single “dynamic” type is fine insofar as any type error would occur at compile time anyway, I wonder if there wouldn’t be a way to maintain future backwards compatibility for finer-grained meta types, as long as the language elements they reflect remain backwards-compatible in the language as well. From first principles, one would think that it should be possible for the backwards compatibility of the reflection system to mirror the backwards compatibility of the reflected language. I’d be interested in the underlying reasons for why this isn’t the case, if any.
PessimalDecimal · 1h ago
Thanks for this link. Between it and the main article, I have a much better sense for how compile time reflection will actually be useful. The syntax is bad enough to make my eyes bleed, but at least they'll bleed for a good reason I hope.
techjamie · 37m ago
> The syntax is bad enough to make my eyes bleed
That's on brand for C++ in general. It works well, but it's ugly as sin while doing it.
112233 · 39m ago
Oh noes, the binding of internal compiler state to STL will become even more severe with this. It started slowly. You needed exact magic std::initializer_list definition in your headers to match the code generated by the compiler, or the program would crash. RTTI (that was of little use to programs that tried to avoid standard library)
Now there are coroutines and this thing. I feel like it is bye-bye to the completely non-standard compliant practice of using C++ without all the standard library.
Where should embedded c++ projects go now that they are not welcome anymore?
jcelerier · 24m ago
> Where should embedded c++ projects go now that they are not welcome anymore?
I'm just using all of this on embedded platforms without issues - and can't wait to use reflection there either, it'll be ultra useful for ESP32 and Teensy projects we're working on
dodomodo · 23m ago
It's not that hard to just copy the relevant part from the standard library of your platform
jasonthorsness · 50m ago
Seems like maybe it will be a challenge to use, but like a lot of template stuff the complexity gets buried in the library. The language gets a lot of ridicule but I like the no-compromise push to help programmers eliminate unnecessary runtime work in their programs.
mystified5016 · 1h ago
Wow. That is... certainly some syntax. It reminds me of Perl.
This syntax is pretty weird even by C++ standards, and it's certainly the worst way to do reflection I've personally seen. But I guess it's good that C++ is finally getting some kind of reflection. Only a few decades late to the party but hey they got there in the end.
Really as C++ grows and evolves, I feel more and more that I'd rather use plain C than wrangle with all of the bizzarro choices C++ has made. C++ is more and more often just the wrong choice of language for anything I want to do. If I need compile-time reflection, I'll use a C# program to generate C code.
nine_k · 1h ago
The comparison with Perl is apt, to my mind. Both Perl and C++ were early to their space, experimenting with concepts that were weird at the time, trying many approaches we now find ugly, and serving as examples of both successes and failures for the much better languages that came after them. The difference is that Perl5 stopped evolving some time ago, while C++ continues the same tendency unabashed.
(Scala is another example of such a language.)
stathibus · 1h ago
Are you suggesting that reflection is a new fancy thing and c++ is paving the way?
PessimalDecimal · 1h ago
> compile-time reflection
> use a C# program to generate C code
These seem at odds.
jcelerier · 22m ago
you call the C# program that generates the code as part of your build system
MoonGhost · 1h ago
How about thin C++ wrapper? The language with the same features, but more human friendly. It should be easily directly translated to C++. Preferably both ways.
sirwhinesalot · 13m ago
That's what Herb Sutter's cppfront/cpp2 is meant to do. Same semantics, sane defaults, nicer syntax (IMO).
layer8 · 38m ago
There are languages like D and Carbon that attempt this. But there are too many existing large C++ code bases to not continue evolving C++ itself as well.
nine_k · 1h ago
C++'s semantics are also broken in interesting ways: UB, implicit conversions, arrays, exceptions, exceptions from destructors, etc. Papering over them won't help all that much. It's more efficient to just swallow the bullet and switch to Rust (or maybe Zig).
jandrewrogers · 47m ago
Many of these inadvisable semantics are fixable in practice, they are just a default that requires additional effort to minimize or eliminate.
That aside, it isn't that easy to switch languages because C++ is more expressive in a systems context in important ways. Porting existing modern systems C++ to e.g. Rust makes this pretty obvious. (I think porting to Zig would likely be a bit easier but I've never actually tried.)
C++ does not win any prizes for being the most aesthetically pleasing programming language but the new syntax around reflection is pretty ugly even by those standards.
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p29...
That's on brand for C++ in general. It works well, but it's ugly as sin while doing it.
I'm just using all of this on embedded platforms without issues - and can't wait to use reflection there either, it'll be ultra useful for ESP32 and Teensy projects we're working on
This syntax is pretty weird even by C++ standards, and it's certainly the worst way to do reflection I've personally seen. But I guess it's good that C++ is finally getting some kind of reflection. Only a few decades late to the party but hey they got there in the end.
Really as C++ grows and evolves, I feel more and more that I'd rather use plain C than wrangle with all of the bizzarro choices C++ has made. C++ is more and more often just the wrong choice of language for anything I want to do. If I need compile-time reflection, I'll use a C# program to generate C code.
(Scala is another example of such a language.)
> use a C# program to generate C code
These seem at odds.
That aside, it isn't that easy to switch languages because C++ is more expressive in a systems context in important ways. Porting existing modern systems C++ to e.g. Rust makes this pretty obvious. (I think porting to Zig would likely be a bit easier but I've never actually tried.)