There's much cooler approach: https://veykril.github.io/tlborm/decl-macros/building-blocks/counting.html#bit-twiddling https://veykril.github.io/tlborm/decl-mac

There's much cooler approach: https://veykril.github.io/tlborm/decl-macros/building-blocks/counting.html#bit-twiddling https://veykril.github.io/tlborm/decl-macros/building-blocks.... macro_rules! count { () => (0); ($odd:tt ($a:tt $b:tt)*) => ((count!($($a)*) << 1) | 1); (($a:tt $b:tt)*) => (count!($($a)*) << 1); } It uses bit twiddling to avoid generating very big AST and eventually crashing the compiler. Though I have to admit using `${count()}` is better.