src/doc/rust-by-example/src/scope/borrow/freeze.md

   1 # Freezing
   2
   3 When data is immutably borrowed, it also *freezes*. *Frozen* data can't be
   4 modified via the original object until all references to it go out of scope:
   5
   6 ```rust,editable,ignore,mdbook-runnable
   7 fn main() {
   8     let mut _mutable_integer = 7i32;
   9
  10     {
  11         // Borrow `_mutable_integer`
  12         let large_integer = &_mutable_integer;
  13
  14         // Error! `_mutable_integer` is frozen in this scope
  15         _mutable_integer = 50;
  16         // FIXME ^ Comment out this line
  17
  18         println!("Immutably borrowed {}", large_integer);
  19
  20         // `large_integer` goes out of scope
  21     }
  22
  23     // Ok! `_mutable_integer` is not frozen in this scope
  24     _mutable_integer = 3;
  25 }
  26 ```