An "or" pattern was used where the variable bindings are not consistently bound
across patterns.
Erroneous code example:
```compile_fail,E0409
let x = (0, 2);
match x {
(0, ref y) | (y, 0) => { /* use y */} // error: variable `y` is bound with
// different mode in pattern #2
// than in pattern #1
_ => ()
}
```
Here, `y` is bound by-value in one case and by-reference in the other.
To fix this error, just use the same mode in both cases.
Generally using `ref` or `ref mut` where not already used will fix this:
```
let x = (0, 2);
match x {
(0, ref y) | (ref y, 0) => { /* use y */}
_ => ()
}
```
Alternatively, split the pattern:
```
let x = (0, 2);
match x {
(y, 0) => { /* use y */ }
(0, ref y) => { /* use y */}
_ => ()
}
```