sum

Live demo is available here.

The StreamExt.sum function returns the sum of the elements as a Future, using the supplied map function to convert each element from the input stream into a num (i.e. either an int or a double).

If a map function is not specified then the identity function is used.

If the closeOnError flag is set to true, then any error in the map function will complete the Future with the error. Otherwise, any errors will be swallowed and excluded from the final sum.