Macro cast_ref

macro_rules! cast_ref {
    (($variable:expr) as $object:ident<$($traits:path),+>) => { ... };
    ($variable:ident as $object:ident<$($traits:path),+>) => { ... };
    (&$variable:ident as $object:ident<$($traits:path),+>) => { ... };
}

A helper macro to downcast a $variable to $object<$network>.