On my machine, the following code runs in 3 seconds in stable version, release build:

// (EDIT: made it compile) fn main() { for i in 0..100000000u32 { let s = i.to_string(); assert!(s.len() > 0); } }

whereas the C++ counterpart runs in 1.2 seconds with -O2:

#include <string> #include <cassert> int main() { for(unsigned int i=0; i<100000000; i++){ std::string s = std::to_string(i); assert(s.size() > 0); } }

I've found that most of the time loss comes from passing &str through a formatter instead of directly memcpying; replacing to_string with _fmt with .to_owned() at the end speeds it up to around 1.6s.