capnpc-macros holds some Rusty macros wrapping capnpc-rust functionality.

For example:

let mut message =
  capnp_new!(address_book::Builder,
    [init_people 2 =>
      [
        [set_id 123]
        [set_name "Alice"]
        [set_email "alice@example.com"]
        [init_phones 1 =>
          [
            [set_number "555-1212"]
            [set_type {person::phone_number::Type::Mobile}]
          ]
        ]
        [init_employment => [set_school "MIT"]]
      ]

      [
        [set_id 456]
        [set_name "Bob"]
        [set_email "bob@example.com"]
        [init_phones 2 =>
          [
            [set_number "555-4567"]
            [set_type {person::phone_number::Type::Home}]
          ]
          [
            [set_number "555-7654"]
            [set_type {person::phone_number::Type::Work}]
          ]
        ]
        [init_employment => [set_unemployed ()]]
      ]
    ]
  );