Macro more_collections::hashsetmultimap

macro_rules! hashsetmultimap {
    (@single $($x:tt)*) => { ... };
    (@count $($rest:expr),*) => { ... };
    ($($key:expr => {$($value:expr),* },)+) => { ... };
    ($($key:expr => {$($value:expr),* }),*) => { ... };
}