Resolution: Won't Do
- Apple Swift version 4.2.1 (swiftlang-1000.11.42 clang-1000.11.45.1)
- Also seems to be present in Swift 5
This is a magical behavior, and it should be disallowed as it's a source of potential ambiguity issues in a more complex project.
Similar example where the default associated type is simply overriden/ignored:
Discussion on the forums: https://forums.swift.org/t/what-kind-of-magic-behavior-is-this/22014