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

I'm excited for this! I tried out Mlem, but it sounds like it isn't being worked on anymore. I'm bootstrapping, so finding communities is pretty important to me. Can't wait to see what you've been putting together.