tests/ui/closures/2229_closure_analysis/run_pass/mut_ref.rs

   1 // edition:2021
   2 // run-pass
   3
   4 // Test that we can mutate a place through a mut-borrow
   5 // that is captured by the closure
   6
   7 // Check that we can mutate when one deref is required
   8 fn mut_ref_1() {
   9     let mut x = String::new();
  10     let rx = &mut x;
  11
  12     let mut c = || {
  13         *rx = String::new();
  14     };
  15
  16     c();
  17 }
  18
  19 // Similar example as mut_ref_1, we don't deref the imm-borrow here,
  20 // and so we are allowed to mutate.
  21 fn mut_ref_2() {
  22     let x = String::new();
  23     let y = String::new();
  24     let mut ref_x = &x;
  25     let m_ref_x = &mut ref_x;
  26
  27     let mut c = || {
  28         *m_ref_x = &y;
  29     };
  30
  31     c();
  32 }
  33
  34 // Check that we can mutate when multiple derefs of mut-borrows are required to reach
  35 // the target place.
  36 // It works because all derefs are mutable, if either of them was an immutable
  37 // borrow, then we would not be able to deref.
  38 fn mut_mut_ref() {
  39     let mut x = String::new();
  40     let mut mref_x = &mut x;
  41     let m_mref_x = &mut mref_x;
  42
  43     let mut c = || {
  44         **m_mref_x = String::new();
  45     };
  46
  47     c();
  48 }
  49
  50 fn main() {
  51     mut_ref_1();
  52     mut_ref_2();
  53     mut_mut_ref();
  54 }