Debugging Combine

print

let publisher = (1...3).publisher

publisher
    .print("DEBUG")
    .sink {
        print($0)
    }

// 출력값
DEBUG: receive subscription: (1...3)
DEBUG: request unlimited
DEBUG: receive value: (1)
1
DEBUG: receive value: (2)
2
DEBUG: receive value: (3)
3
DEBUG: receive finished