Macro slice_ 

macro_rules! slice_ {
    ($($elem:expr),* $(,)?) => { ... };
    (: $($elem:expr),*) => { ... };
    ($t:ty : $($elem:expr),*) => { ... };
    ($f:ident : $($elem:expr),*) => { ... };
}

Map a function over the elements of a []. By default, .to_string() is applied. To specify the mapping, a function or type followed by | can precede the elements. The pure prefix : is shorthand for calling .into().