02 · Switch Case — multi-way conditional routing

What this lesson demonstrates

Where 01_edge_condition forked into two branches with a pair of conditional edges, this lesson uses the higher-level switch builder to fan out into three mutually-exclusive branches. The detection step now returns a three-way SpamDecision — NotSpam, Spam, or Uncertain — and a switch with two cases plus a default routes the message to exactly one downstream executor.

A switch is sugar over conditional edges: it builds one fan-out edge whose assigner picks a single target per message, and it guarantees a fallback so nothing is dropped.

The real code

b := workflow.NewBuilder(detect)
b.AddSwitch(detect).
    AddCase(func(msg any) bool { return msg.(DetectionResult).Decision == NotSpam }, assistant).
    AddCase(func(msg any) bool { return msg.(DetectionResult).Decision == Spam }, spam).
    WithDefault(uncertain).
    AddToBuilder(b).
    AddEdge(assistant, send).             // unconditional: chain send after assistant
    WithOutputFrom(send, spam, uncertain) // every terminal is a workflow output

AddSwitch opens the switch on detect; each AddCase(pred, target) is a case; WithDefault(uncertain) is the fall-through. AddToBuilder(b) commits the switch back onto the builder so you can continue chaining plain edges.

What to notice

• The default is not optional in spirit. With plain conditional edges you can drop a message if no predicate matches. A switch with WithDefault guarantees exactly one branch always fires — here, Uncertain emails land in the review queue rather than vanishing.
• AddToBuilder(b) is the join back. The switch is built on a sub-builder; you must commit it with AddToBuilder before the outer builder sees those edges. Forgetting it silently leaves the branches unwired.
• Cases are evaluated in order. The first matching predicate wins, so order your AddCase calls from most specific to least.
• Classification stays a plain function. detectEmail is a normal func(string) DetectionResult, kept outside the executor so both the node and the tests reason about it directly.

How it maps to the Agent Framework

In the Microsoft Agent Framework Go SDK, AddSwitch/AddCase/WithDefault is the ergonomic way to express deterministic routing in a workflow graph — the kind of dispatch you’d otherwise hand-roll with several AddDirectEdge calls and a manually-maintained “else” edge. When you later route between Azure AI Foundry agents (“send billing questions to the finance agent, everything else to the general agent”), this is the construct you reach for. It stays fully offline here because the classifier is a pure function, not a model call.

Run it

go run ./tutorial/03-workflows/conditional-edges/02_switch_case

Fully offline. The built-in input mentions “invoice”, so the detector returns Uncertain and the switch’s default branch routes it to HandleUncertainExecutor.

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