// OLD
struct CustomCall: ReactiveCall { ... }

let client = CustomClient()
let call = CustomCall()

// 1
call.rx
    .response(with: client)
    ...

// 2
call.rx
    .values(with: client)
    ...

// NEW
struct CustomCall: Call { ... }

let client = CustomClient()
let session = Session(with: client)
let call = CustomCall()

// 1
session
    .start(call: call)
  
// 2
session
    .start(call: call)
    .map(\.value)