///
/// ```
/// assert_eq!(["hello", "world"].concat(), "helloworld");
+ /// assert_eq!([[1, 2], [3, 4]].concat(), [1, 2, 3, 4]);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
fn concat(&self) -> Self::Output;
///
/// ```
/// assert_eq!(["hello", "world"].join(" "), "hello world");
+ /// assert_eq!([[1, 2], [3, 4]].join(&0), [1, 2, 0, 3, 4]);
/// ```
#[stable(feature = "rename_connect_to_join", since = "1.3.0")]
fn join(&self, sep: &T) -> Self::Output;