Macro zerocopy_type 

macro_rules! zerocopy_type {
    (
        $(#[$meta:meta])*
        $vis:vis struct $name:ident($inner_vis:vis $t:ty) $(;)?
    ) => { ... };
    (
        $(#[$meta:meta])*
        $vis:vis struct $name:ident {
            $inner_vis:vis $inner_name:ident: $t:ty $(,)?
        }
    ) => { ... };
}

Macro which declares a zerocopy-flavored type, which can be used in a field

The type implements all of the required derive traits, as well as HeaderLen and Emit.