on

Labels each edge that a call to Deps.Flow.before or Deps.Flow.after draws between the call's receiver and first or one of rest.

Each edge of a fan-out can therefore carry its own label, and one label can go on several edges:

checked.before(Label.of("rows found").on(processed), Label.of("no rows").on(reportEmpty));
// load >> Label("forks") >> [report_empty, report_suspicious]
loaded.before(Label.of("forks").on(reportEmpty, reportSuspicious));

Passing a task's handle into another task's arguments declares an edge. Calling Then, Else or Case also declares an edge. To label one of those edges, declare it again with a label. Declaring an edge again only applies the label. A new label replaces the label the edge had, as Python's DAG.set_edge_info does. Declaring the edge again without a label keeps its label.

When an edge goes to or from a task group, the UI draws it to or from the group's own node and shows the label there. A label never changes which tasks an edge connects. Python's Label can change those tasks. It does so when the end written to the left of the Label is in a task group and the other end is not in that same group. Python then replaces the left end with the group that contains it. For example, if v is in group g and n is in no group, v >> Label("x") >> n draws edges from the last tasks in g instead of from v. In Java, the end that matches this left end is the receiver of Deps.Flow.before or Deps.Flow.after.

Parameters