exit status: 1 with stderr:
<stdin>:7:8: error: type 'S<T>' does not conform to protocol 'P' struct S<T>: P { ^ <stdin>:10:9: note: candidate has non-matching type 'T' var a: T { return value } ^ <stdin>:4:9: note: protocol requires property 'a' with type 'S<T>.A?'; do you want to add a stub? var a: A? { get } ^