futures-definitions.chalk

struct Result<T, E> { }

trait Future {
  type Output;
}

trait FutureResult
where
  Self: Future<
    Output = Result<
      <Self as FutureResult>::Item,
      <Self as FutureResult>::Error
    >
  >
{
  type Item;
  type Error;
}

impl<T, I, E> FutureResult for T
where T: Future<Output = Result<I, E>>
{
  type Item = I;
  type Error = E;
}

struct u32 { }

struct Error { }

struct MyFuture1 { }

impl Future for MyFuture1 {
  type Output = u32;
}

struct MyFuture2 { }

impl Future for MyFuture2 {
  type Output = Result<u32, Error>;
}