compiler/rustc_error_codes/src/error_codes/E0070.md

   1 An assignment operator was used on a non-place expression.
   2
   3 Erroneous code examples:
   4
   5 ```compile_fail,E0070
   6 struct SomeStruct {
   7     x: i32,
   8     y: i32,
   9 }
  10
  11 const SOME_CONST: i32 = 12;
  12
  13 fn some_other_func() {}
  14
  15 fn some_function() {
  16     SOME_CONST = 14; // error: a constant value cannot be changed!
  17     1 = 3; // error: 1 isn't a valid place!
  18     some_other_func() = 4; // error: we cannot assign value to a function!
  19     SomeStruct::x = 12; // error: SomeStruct a structure name but it is used
  20                         //        like a variable!
  21 }
  22 ```
  23
  24 The left-hand side of an assignment operator must be a place expression. A
  25 place expression represents a memory location and can be a variable (with
  26 optional namespacing), a dereference, an indexing expression or a field
  27 reference.
  28
  29 More details can be found in the [Expressions] section of the Reference.
  30
  31 [Expressions]: https://doc.rust-lang.org/reference/expressions.html#places-rvalues-and-temporaries
  32
  33 And now let's give working examples:
  34
  35 ```
  36 struct SomeStruct {
  37     x: i32,
  38     y: i32,
  39 }
  40 let mut s = SomeStruct { x: 0, y: 0 };
  41
  42 s.x = 3; // that's good !
  43
  44 // ...
  45
  46 fn some_func(x: &mut i32) {
  47     *x = 12; // that's good !
  48 }
  49 ```