Macro impl_obs_drop

macro_rules! impl_obs_drop {
    ($struct_name: ident, $operation:expr) => { ... };
    ($struct_name: ident, ($($var:ident),* $(,)*), $operation:expr) => { ... };
    (is_runtime, $struct_name: ident, ($($var:ident),* $(,)*), $operation:expr) => { ... };
}