Error code E0642

Trait methods currently cannot take patterns as arguments.

Erroneous code example:

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!
}