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by spacechild1 16 days ago
> Rust's metaprogramming capabilities are now on par with C++ (they weren't always).

Is that really true, though? I haven't really written any Rust code, so I have no idea, but I don't think Rust has static reflection. Also, aren't const generics much more limited? I've also heard there is no template specialization and no "if constexpr". Or what about dynamic allocations in constexpr functions?
1 comments
cogman10 16 days ago
> I don't think Rust has static reflection.

Before C++ in fact through procedural macros. You can do everything you can do with C++ static reflection.

Now, it could be better. Proc macros require you to pull in secondary packages for parsing the token stream. But all the sorts of operations you can do via static reflection you can do via proc macros. That's how the most popular rust serialization package like serde works. It's also how some more popular database libs work like sqlx.

> Also, aren't const generics much more limited? I've also heard there is no template specialization and no "if constexpr".

Both have been added and expanded. AFAIK they are now roughly on par with what C++ const expressions can do. What they can't do, proc macros can do.

> Or what about dynamic allocations in constexpr functions?

IDK if that's possible in rust. Const expr capabilities of rust have been rapidly expanding though in the last year.

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spacechild1 16 days ago
> You can do everything you can do with C++ static reflection.

Are you really sure about that?

I have a slight problem with such sweeping statements and also with your original claim that "Rust's metaprogramming capabilities are now on par with C++". I think you can only make such claims if you know both languages really, really well.

That being said, I acknowledge that Rust's metaprogramming capabilities have improved significantly in recent years.

> Both have been added and expanded.

In stable Rust?

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dwattttt 16 days ago
It's hard to be concrete without talking about something specific. At the limit, in stable Rust (for 8 years?), a proc_macro consumes and emits an arbitrary token stream at compile time; it's not ergonomic, but it's possible.

The equivalent in C++ is in the realm of arbitrary codegen.

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