The parameters of any trait method must match between a trait implementation and the trait definition.
Erroneous code example:
trait Foo {
fn foo(x: u16);
fn bar(&self);
}
struct Bar;
impl Foo for Bar {
// error, expected u16, found i16
fn foo(x: i16) { }
// error, types differ in mutability
fn bar(&mut self) { }
}