Macro memoffset::span_of

macro_rules! span_of {
    (@helper $root:ident, [] ..=) => { ... };
    (@helper $root:ident, [] ..) => { ... };
    (@helper $root:ident, [] ..= $($field:tt)+) => { ... };
    (@helper $root:ident, [] .. $($field:tt)+) => { ... };
    (@helper $root:ident, $(# $begin:tt)+ [] ..= $($end:tt)+) => { ... };
    (@helper $root:ident, $(# $begin:tt)+ [] .. $($end:tt)+) => { ... };
    (@helper $root:ident, $(# $begin:tt)+ [] ..) => { ... };
    (@helper $root:ident, $(# $begin:tt)+ [] ..=) => { ... };
    (@helper $root:ident, $(# $begin:tt)+ []) => { ... };
    (@helper $root:ident, $(# $begin:tt)+ [] $tt:tt $($rest:tt)*) => { ... };
    (@helper $root:ident, [] $tt:tt $($rest:tt)*) => { ... };
    ($sty:ty, $($exp:tt)+) => { ... };
}