How to encode objects of unknown type?

[manfred (Manfred Schubert)]

@hamishknight

This exploits the fact that existentials (protocol-typed values) are “opened” when you call a method on them, which gives the extension implementation access to the underlying concrete type, which can then be used to satisfy the T : Encodable placeholder for the single value container’s encode(_:) method.

Thanks a lot, this works now. I have to admit though, that I don't understand why and how.

Is there a place where I can read up on existentials and this topic?