use crateFuture;
use crateStream;
/// Trait to represent types that can be created by summing up a stream.
///
/// This trait is used to implement the [`sum`] method on streams. Types which
/// implement the trait can be generated by the [`sum`] method. Like
/// [`FromStream`] this trait should rarely be called directly and instead
/// interacted with through [`Stream::sum`].
///
/// [`sum`]: trait.Sum.html#tymethod.sum
/// [`FromStream`]: trait.FromStream.html
/// [`Stream::sum`]: trait.Stream.html#method.sum