Type Annotations

Annotations

In certain cases, the type of an expression cannot be properly inferred by the compiler. In order to help the type checker, you can annotate an expression with its desired type. Here is an example:

cameligo

type parameter = Back | Claim | Withdraw

type storage = {
  owner    : address;
  goal     : tez;
  deadline : timestamp;
  backers  : (address, tez) map;
  funded   : bool
}

[@entry]
let back (param : unit) (store : storage) : operation list * storage = (* Annotation *)
  if Tezos.get_now () > store.deadline then failwith "Deadline passed."
  else
    match Map.find_opt (Tezos.get_sender ()) store.backers with
      None ->
        let backers = Map.update (Tezos.get_sender ()) (Some (Tezos.get_amount ())) store.backers
        in [], {store with backers=backers}
    | Some (x) -> [], store

jsligo

type parameter =
  ["Back"]
| ["Claim"]
| ["Withdraw"];

type storage = {
  owner    : address,
  goal     : tez,
  deadline : timestamp,
  backers  : map<address, tez>,
  funded   : bool
};

@entry
const back = (param : unit, store : storage) : [list<operation>, storage] => { // Annotation
  let no_op = list([]);
  if (Tezos.get_now() > store.deadline) {
    return failwith ("Deadline passed.");
  }
  else {
    return match(Map.find_opt (Tezos.get_sender(), store.backers)) {
      when(None()): do {
        let backers = Map.update(Tezos.get_sender(), Some(Tezos.get_amount()), store.backers);
        return [no_op, {...store, backers:backers}];
      };
      when(Some(x)): [no_op, store]
    }
  };
};