src/librustc_error_codes/error_codes/E0505.md

   1 A value was moved out while it was still borrowed.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0505
   6 struct Value {}
   7
   8 fn borrow(val: &Value) {}
   9
  10 fn eat(val: Value) {}
  11
  12 fn main() {
  13     let x = Value{};
  14     let _ref_to_val: &Value = &x;
  15     eat(x);
  16     borrow(_ref_to_val);
  17 }
  18 ```
  19
  20 Here, the function `eat` takes ownership of `x`. However,
  21 `x` cannot be moved because the borrow to `_ref_to_val`
  22 needs to last till the function `borrow`.
  23 To fix that you can do a few different things:
  24
  25 * Try to avoid moving the variable.
  26 * Release borrow before move.
  27 * Implement the `Copy` trait on the type.
  28
  29 Examples:
  30
  31 ```
  32 struct Value {}
  33
  34 fn borrow(val: &Value) {}
  35
  36 fn eat(val: &Value) {}
  37
  38 fn main() {
  39     let x = Value{};
  40
  41     let ref_to_val: &Value = &x;
  42     eat(&x); // pass by reference, if it's possible
  43     borrow(ref_to_val);
  44 }
  45 ```
  46
  47 Or:
  48
  49 ```
  50 struct Value {}
  51
  52 fn borrow(val: &Value) {}
  53
  54 fn eat(val: Value) {}
  55
  56 fn main() {
  57     let x = Value{};
  58
  59     let ref_to_val: &Value = &x;
  60     borrow(ref_to_val);
  61     // ref_to_val is no longer used.
  62     eat(x);
  63 }
  64 ```
  65
  66 Or:
  67
  68 ```
  69 #[derive(Clone, Copy)] // implement Copy trait
  70 struct Value {}
  71
  72 fn borrow(val: &Value) {}
  73
  74 fn eat(val: Value) {}
  75
  76 fn main() {
  77     let x = Value{};
  78     let ref_to_val: &Value = &x;
  79     eat(x); // it will be copied here.
  80     borrow(ref_to_val);
  81 }
  82 ```
  83
  84 You can find more information about borrowing in the rust-book:
  85 http://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html