For each notification in the source sequence, SelectMany constructs and subscribes to the results of an asynchronous operation specified in the nested workflow. If multiple asynchronous operations are launched simultaneously, SelectMany will merge all the results into a single sequence.

The input to the nested workflow represents the element passed as an argument to the asynchronous operation. If the input is itself an observable sequence, the WorkflowInput node will subscribe to all the values in the sequence when the asynchronous operation is launched. Otherwise, the input will emit a single value containing the stored argument value.

Tip

SelectMany is one of the most versatile reactive operators and can be used as a primitive building block on which to build a large number of more complex reactive operators, including reactive state machines. See the State Machines tutorial for examples.