Ok, i'm starting to understand what we're disagreeing on. You're talking about pattern matching with dynamic expressions ( don't know the official name for that), such as what you find in erlang, i'm talking very basic enum unwrapping based on types, which is compile time checked. Swift also adds some kind of dynamic expression to patterns, which may break exhaustiv checking, but in the case of go, just a simple type check would be a great start.

Edit ( since i can't reply) : just look at https://developer.apple.com/library/content/documentation/Sw... with something like the barcode example.

It's all compile time checked.