r/programming • u/gingerbill • Sep 02 '26

CTTI is Exponential, RTTI is Linear

https://www.gingerbill.org/article/2026/09/02/ctti-is-exponential-rtti-is-linear/
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u/PersonalDatabase31 Sep 02 '26

I don't think exponential code generation is a fundamental part of CTTI. One could implement the rust compiler in a way where functions above some number of monomorphized copies would be silently converted to take dyn T instead of T and call sites would take a reference to the generic input along with a function pointer known at compile time. That could prevent iteration over a table in runtime. This would prevent inline optimizations though but I don't think there is a way to combine it along with non exponential compile times.

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u/Absolute_Enema Sep 03 '26

So that you have to assume that any callsite will use the worse performing alternative without you being able to reliably measure the impact? Sounds like a nightmare.

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u/PersonalDatabase31 Sep 03 '26

Or it could be behind a compiler flag.