anchor.diff:  
   Potentially better performance:: Consider the following function:
   +
  -[source,rust]
  +[source]
   ----
   fn f(a: &mut u8, b: &mut u8, g: fn()) {
       mem::swap(a, b);
  
positive.code: 
  No exception unsafety:: Consider the following (incorrect) rust code:
  +
  ----
  fn push(a: &mut Vec<T>, g: fn() -> T) {
      unsafe {
  
negative.code: compiler, the user doesn't have to bother with annoying annotations. For
  example, the following lrs program can be compiled as written:
  
  [source]
  ----
  use std::tty::{is_a_tty};
  
  