1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
use std::ops::{Index, IndexMut}; struct S; struct H; impl S { fn f(&mut self) {} } impl Index<u32> for H { type Output = S; fn index(&self, index: u32) -> &S { unimplemented!() } } impl IndexMut<u32> for H { fn index_mut(&mut self, index: u32) -> &mut S { unimplemented!() } } fn main() { H["?"].f(); //~ ERROR mismatched types }