More digging revealed this is a bug in 0.5.0, closed in 0.6.0 (http://
github.com/ffi/ffi/issues/closed#issue/12).

On Dec 30 2009, 12:17 pm, Simon Chiang <simon.a.chi...@gmail.com>
wrote:

> As an FYI, this raises a TypeError ('wrong argument type Class
> (expected Data)'):
>
>       class Field < FFI::Struct
>         layout :type, :ushort, :value, :pointer
>       end
>       class Multifield < FFI::Struct
>         layout :theFields, [Field, 1]
>       end
>
> On Dec 30, 10:37 am, Simon Chiang <simon.a.chi...@gmail.com> wrote:
>

> > How can I layout structures like this?

>

> >   struct field
> >     {
> >      unsigned short type;
> >      void *value;
> >     };

>

> >   struct multifield
> >     {
> >      struct field theFields[1];
> >     };

>

> > If theFields was another type, say a pointer, then I'd try something
> > like this (although I'm not sure if this would be correct either):

>

> >       class Field < FFI::Struct
> >         layout :type, :ushort, :value, :pointer
> >       end
> >       class Multifield < FFI::Struct
> >         layout :theFields, [:pointer, 1]
> >       end

>

> > How can I specify 'struct field' as a type?