> For example, instead of a power function that uses a loop, you could generate specialized code like x * x * x * x * x directly. This eliminates runtime overhead and creates highly optimized code.
This is misguided. For decennia now, there is no reason to assume that hand-unrolled code is faster than a for-loop. Compilers optimize this stuff, and they do this even better than mindlessly multiplying x by itself. For example, raising x to the power 6 only needs 3 multiplications, see for example: https://godbolt.org/z/Edz4jjqvv
While there are definitely use cases for meta-programming, optimization is not one of them.
kldx · 4h ago
> For example, instead of a power function that uses a loop, you could generate specialized code like x * x * x * x * x directly. This eliminates runtime overhead and creates highly optimized code.
Could anyone explain to me how this is different from templates or parameter pack expansion in C++? I can see the constexpr-ness here is encoded in the type system and appears more composable, but I am not sure if I am missing the point.
I looked at the paper but I can't find anything related to C++.
gsliepen · 51m ago
> Could anyone explain to me how this is different from templates or parameter pack expansion in C++?
I don't think it's any different.
> I can see the constexpr-ness here is encoded in the type system
I also see they introduce new constructs like let$, so it's not just a type system thing.
> I looked at the paper but I can't find anything related to C++.
I don't think the author needs to compare their code to C++. That said, it looks to me like it is similar to the upcoming C++26's reflection capabilities.
TimorousBestie · 6h ago
This is fascinating. I could see it being very useful for writing SIMD abstraction layers (like Highway or SIMDe) without so much of the cruft.
perihelions · 3h ago
How is this different from a syntactic macro?
burakemir · 2h ago
Two big differences:
- it is typed, and
- multi-stage programming can also describe runtime-code generation.
This is misguided. For decennia now, there is no reason to assume that hand-unrolled code is faster than a for-loop. Compilers optimize this stuff, and they do this even better than mindlessly multiplying x by itself. For example, raising x to the power 6 only needs 3 multiplications, see for example: https://godbolt.org/z/Edz4jjqvv
While there are definitely use cases for meta-programming, optimization is not one of them.
Could anyone explain to me how this is different from templates or parameter pack expansion in C++? I can see the constexpr-ness here is encoded in the type system and appears more composable, but I am not sure if I am missing the point.
I looked at the paper but I can't find anything related to C++.
I don't think it's any different.
> I can see the constexpr-ness here is encoded in the type system
I also see they introduce new constructs like let$, so it's not just a type system thing.
> I looked at the paper but I can't find anything related to C++.
I don't think the author needs to compare their code to C++. That said, it looks to me like it is similar to the upcoming C++26's reflection capabilities.