About conforming types you don't own to protocols you don't own

[cukr]

@Jens

For example this seems harmless to me (but perhaps it isn't?)

It's harmless until Apple decides to also make them ExpressibleByArrayLiteral, and you update the OS. Which conformance will be used? The one defined in Foundation, or the one defined in your code? What if one of the libraries you use adds the same conformance?

If you own either the type, or the protocol, you will be able to make sure that there's only one conformance

@Jens

But I'd like to see a more in depth discussion.

Here's a thread talking about it Retroactive Conformances vs. Swift-in-the-OS