Macro arch_struct_with_union 

macro_rules! arch_struct_with_union {
    ($arch:expr, $ty:ident { $($token:tt)* }) => { ... };
}

Initializes the given fields of a struct or union and returns the union as a ArchSpecificUnionContainer.

arch_struct_with_union is invoked like struct_with_union_into_bytes, but the first parameter of the macro must be an expression returning an ArchSpecific used to decide which macro to instantiate.