03 · Multi-Selection Fan-Out (edge assigner)

What this lesson demonstrates

A conditional edge is one true/false gate per edge, and a switch picks exactly one branch. This lesson goes further: a single analysis executor fans out to many targets, and an edge assigner chooses which subset each message goes to. Unlike default fan-out — which delivers to every target — the assigner can select several targets at once.

Concretely: a “not spam” email always goes to the assistant branch, and additionally to the summary branch when it is long. One message, two destinations.

The real code

The assigner is a func(int, any) iter.Seq[int] that yields the indexes of the targets a message should reach:

func routeAnalysis(_ int, msg any) iter.Seq[int] {
    return func(yield func(int) bool) {
        result := msg.(AnalysisResult)
        switch result.Decision {
        case Spam:
            yield(0) // spam
        case NotSpam:
            if !yield(1) { // assistant
                return
            }
            if result.EmailLength > longEmailThreshold {
                yield(2) // summary — assistant AND summary
            }
        case Uncertain:
            yield(3) // uncertain
        }
    }
}

It is attached with AddFanOutEdge(analyze, targets, workflow.WithEdgeAssigner(routeAnalysis)). The target slice order — spam, assistant, summary, uncertain — is what the yielded indexes refer to.

What to notice

• Indexes, not conditions. The assigner yields into the target slice by position, so the order you pass to AddFanOutEdge is load-bearing. A reordered slice silently reroutes everything.
• Yielding more than once is the whole point. NotSpam yields 1 and, for long emails, 2 — the multi-selection case. Yield zero indexes and the message is dropped for that edge.
• It composes with a plain conditional edge. Alongside the fan-out, a separate AddDirectEdge(analyze, log, false, ...) audits short emails straight to the database. Assigners and conditional edges coexist on the same source node.
• iter.Seq[int] respects back-pressure. The yield returns a bool; honoring it (the if !yield(1) { return }) is the idiomatic Go 1.23 range-over-func pattern.

How it maps to the Agent Framework

In the Microsoft Agent Framework Go SDK, WithEdgeAssigner is how you express “route this to whichever handlers apply” rather than “route to exactly one”. That’s the shape of real dispatch: a document might need both translation and summarization, or an alert might go to logging and an on-call agent. Because the classifier here is a pure function, the lesson stays fully offline — but swapping it for an Azure AI Foundry agent that emits a structured decision needs no change to the routing.

Run it

go run ./tutorial/03-workflows/conditional-edges/03_multi_selection

Fully offline. The built-in email is long and ordinary, so the assigner routes it to both the assistant and summary branches and the workflow yields multiple outputs.

Next: human_in_the_loop_basic · A Workflow That Asks a Human