Swift version 4.1 (swift-4.1-RELEASE)/usercode/main.swift:7:1: error: type 'X<T>' does not conform to protocol 'B' extension X: D where T == Int { // Type 'X<T>' does not conform to protocol 'B' ^ /usercode/main.swift:4:10: note: type 'X<T>' does not conform to inherited protocol 'B' protocol D: B, C {} ^