Dictionary is a value type so it is stack-allocated. But that value is a pretty thin wrapper around a heap-allocated backing store. I’m not sure how useful it is to think about or even know that detail. I hate doing the cliché thing here, but can I ask why you are asking?

If anyone has any feedback on the content, I'd love to hear! You can also check out the sources and even get involved here: https://github.com/apple/swift-migration-guide