4 let x = std::sync::Mutex::new(1usize);
6 //~^ ERROR invalid left-hand side of assignment
7 x.lock().unwrap() += 1;
8 //~^ ERROR binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`
10 let mut y = x.lock().unwrap();
12 //~^ ERROR mismatched types
14 //~^ ERROR binary assignment operation `+=` cannot be applied to type `MutexGuard<'_, usize>`