Nested Codable Protocols with Swift 4

Question

I played a bit with Swift 4 and Codable and got stuck in a script with nested protocols that all conform to Codable .

A simplified example is as follows:

 protocol CodableSomething: Codable {} protocol CodableAnotherThing: Codable { var something: CodableSomething { get } } struct Model: CodableAnotherThing { var something: CodableSomething } 

This code generates build errors using Xcode 9 Beta 5:

• Type 'Model' does not comply with 'Decodable' protocol
• Type 'Model' does not comply with the protocol 'Encodable'

Now I did not expect these errors, because I realized that compliance with these protocols would be automatically generated by the compiler, when in fact I could not even implement this correspondence manually without assembly errors. I also tried several different approaches to solving this nested model structure using Codable , but I just couldn't get it to work.

My question is : Is this a compiler bug (still beta) or am I something wrong?