C. When to use Custom Gatherer?.md

When Should You Use Custom Gatherer?

Avoid custom Gatherer unless necessary—prefer built-in operations first.

Use a custom Gatherer when:

1. map, filter, or flatMap don't fit your logic
2. Built-in Gatherers (like scan or windowFixed) don't solve it
3. You need stateful, cross-element logic that's hard to express otherwise

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← What is a Gatherer?

[Inbuilt Gatherers](D. Inbuilt Gatherers.md)→