Macro declare 

macro_rules! declare {
    ($ty:ty {
        id: $id:expr,
        version: $version:expr,
        policy: $policy:expr,
        response: $response:ty
        $(, input: $input:ty)?
        $(, output: $output:ty)?
        $(, description: $description:expr)?
        $(, visibility: $visibility:expr)?
        $(, replay: $replay:expr)?
        $(, grpc: ($package:expr, $service:expr, $method:expr))?
        $(, grant: $grant:expr)?
        $(, key: $key:expr)?
        $(,)?
    }) => { ... };
    (@direction) => { ... };
    (@direction $item:ty) => { ... };
}