class C<T>: NSObject {
    
    let t: T
    
    init(t: T) {
        self.t = t
    }
    
    class func f<U>() -> (U) -> () where U: C  {
        return { (u: U) in 
            print(u.a) // this is fine because it doesn't involve `U` at all
            print(u.t) // this line crashes
            print(U.self) // this line would crash if it was reached
        }
    }
    
    class func g<U>(_ u: U) where U: C  {
        print(u.t)
    }

}

class Irrelevant {
    
}

let c = C(t: Irrelevant())
C.g(c) // fine
C.f()(c) // crashes on ARM