Imitates push semantics by automatically pulling side-effects from given arg.

Represents sum of multiple .addStage(…)'s and/or .addPipeline(…)'s acting on messages .put(…) into it. .fork(…) can be used to have multiple instances of the same set of Stage's. No stage execution occur unless async iteration happens on the pipeline (and values are .put(…) into it).

Produces a Stage that runs branchArg for each unique .pickKey(…) result.

Prevents AsyncIterable from being done when exiting the loop on it.

Async generator function that is supposed to: