pub trait ShouldBeArgs<T> {
type MessageT: Display;
// Required method
fn expected(&self) -> &T;
// Provided method
fn message(&self) -> Option<&Self::MessageT> { ... }
}pub trait ShouldBeArgs<T> {
type MessageT: Display;
// Required method
fn expected(&self) -> &T;
// Provided method
fn message(&self) -> Option<&Self::MessageT> { ... }
}