Class Ensure

future-java/src/main/java/io/trane/future/Promise.java:611–622

  }

  private static class Ensure<T> extends Continuation<T, T> {
    private final Runnable f;

    public Ensure(final Runnable f) {
      this.f = f;
    }

    @Override
    final Future<T> apply(final Future<T> result) {
      return result.ensure(f);
    }
  }

  @Override
  public final Future<T> ensure(final Runnable f) {