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Comment by nullpoint420 | Hacker News Reader

Wow that’s gnarly it’s using dynamic dispatch. I mean I get it, but I thought zig was some sort of performance demon.

if youre doing io, one pointer indirection seems unlikely tp be rate limiting. same for allocation (the other dynamic dispatch in zig)

It's not just I/O, it's also mutexes, condition variables, time, etc. It's not horrible, but it does add up, so calling it super efficient is a stretch.

A modern allocator with per-thread cache can satisfy some allocations in 20-30 cycles - dynamic dispatch can easily double that, even if the target is still in cache.

It's one of these things where it's extremely use case dependant - like many performance issues, you probably don't care about it - but when you do it matters.

Inderect call cost is a few cycles, if predicted. Now, you can argue, that it may be mispredicted and misprediction would cost about 20-30 cycles. But if it is mispredicted, then you are not calling into allocator often enough. And if you don't hammer it hard, then why do you care about preformance?

I believe their plan is using "restricted function pointers", where you can specify that a pointer will only ever be to a function defined in the codebase. I'm pretty sure they also have plans for devirtualization, but I haven't followed super closely.

"you can specify that a pointer"

i dont think you need to specify that. the compiler can figure it out and do an optimization pass at the end.

Oh, is it not a specific keyword? I thought they were thinking of it being a keyword so you could be sure that it was restricted, in case a variable or function was exported that took in a foreign pointer.

There are going to be builtins to control this. The compiler will not do it on its own.

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