Expected type did not match the received type.

Erroneous code example:

```compile_fail,E0308
let x: i32 = "I am not a number!";
//     ~~~   ~~~~~~~~~~~~~~~~~~~~
//      |             |
//      |    initializing expression;
//      |    compiler infers type `&str`
//      |
//    type `i32` assigned to variable `x`
```

This error occurs when the compiler is unable to infer the concrete type of a
variable. It can occur in several cases, the most common being a mismatch
between two types: the type the author explicitly assigned, and the type the
compiler inferred.
