Type Alias InterfaceGuard<T>

Characterize dynamic behavior such as method argument/response signatures and promise awaiting.

The @endo/exo! package uses InterfaceGuards as the first level of defense for Exo objects against malformed input.

For example:

const AsyncSerializerI = M.interface('AsyncSerializer', {
  // This interface has a single method, which is async as indicated by M.callWhen().
  // The method accepts a single argument, consumed with an implied `await` as indicated by M.await(),
  // and the result of that implied `await` is allowed to fulfill to any value per M.any().
  // The method result is a string as indicated by M.string(),
  // which is inherently wrapped in a promise by the async nature of the method.
  getStringOf: M.callWhen(M.await(M.any())).returns(M.string()),
});
const asyncSerializer = makeExo('AsyncSerializer', AsyncSerializerI, {
  // M.callWhen() delays invocation of this method implementation
  // while provided argument is in a pending state
  // (i.e., it is a promise that has not yet settled).
  getStringOf(val) { return String(val); },
});

const stringP = asyncSerializer.getStringOf(Promise.resolve(42n));
isPromise(stringP); // => true
await stringP; // => "42"
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