library test;

import 'dart:async';

class MyFuture<T> implements Future<T> {
  MyFuture() {}
  MyFuture.value(T x) {}
  MyFuture<S> then<S>(FutureOr<S> f(T x), {Function? onError}) => throw '';
  dynamic noSuchMethod(invocation) => null;
}

main() {}
void test(MyFuture f) {}