Macro io_struct_impl 

macro_rules! io_struct_impl {
    (
        $name:ident ( $( $param:ident : $ty:ty ),* ) -> $reply:ty, $entry_id:expr, $interface_id:expr
    ) => { ... };
    (
        $name:ident ( $( $param:ident : $ty:ty ),* ) -> $reply:ty | $throws:ty, $entry_id:expr, $interface_id:expr
    ) => { ... };
    (
        $name:ident ( $( $param:ident : $ty:ty ),* ) -> $reply:ty $( | $throws:ty )?, $entry_id:expr
    ) => { ... };
    (
        @impl_base $name:ident ( $( $param:ident : $ty:ty ),* ) -> $reply:ty, $entry_id:expr, $interface_id:expr
    ) => { ... };
}