Trait methods currently cannot take patterns as arguments.
Example of erroneous code:
```compile_fail,E0642
trait Foo {
fn foo((x, y): (i32, i32)); // error: patterns aren't allowed
// in trait methods
}
```
You can instead use a single name for the argument:
```
trait Foo {
fn foo(x_and_y: (i32, i32)); // ok!
}
```