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    I’ve wondered whether it would be possible to work with immutable code versions - I remember reading something along those lines in Erlang? Keep the version as part of the type. If MyClass has a field of type YourClass then it knows which version of it it is, and if you release a new version of YourClass then I keep using the old one until I release a new version of MyClass, and code tries to mismatch versions of YourClass then it’ll be a compile error (or there could be an adapter typeclass or some such).

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      This is true in Rust at least. We allow you to include two incompatible versions of transitive dependencies, as they should be internal But sometimes they’d leak through into a public interface, and then you’d get a very confusing error “expected type Foo, got type Foo”. The ecosystem has learned some lessons and people are more careful about this kind of thing now.