Consider following functions

pub fn unwrap_combinators(a: Option<i32>, b: i32) -> bool { a.map(|t| t >= b) .unwrap_or(false) } pub fn unwrap_manual(a: Option<i32>, b: i32) -> bool { match a { Some(t) => t >= b, None => false } }

The first pattern is what we often write and the second one is the most efficient manually unrolled version. Surprisingly rustc fails to optimize the former one into the latter as you can see in godbolt listing:

example::unwrap_combinators:  xor eax, eax  cmp edx, esi  setle al  test edi, edi  mov ecx, 2  cmovne ecx, eax  cmp cl, 2  setne al  and al, cl  ret example::unwrap_manual:  test edi, edi  setne cl  cmp esi, edx  setge al  and al, cl  ret

P.S. Yes, I'm aware of map_or