arrow ensure doesn't make value non nullable after check

Question

have a question about ensure function, somehow it doesn't make null safe after check in either block. What I am doing wrong, or is there a better way to ensure that value is not null except of using !! here is my code

 suspend fun checkCanConnectDirectChat(
    senderId: Int?,
    receiverId: Int?,
    chatRoomId: Int?
  ) = either {
    ensure(chatRoomId != null && receiverId != null) {
      BadRequestExceptionResponse(message = ErrorConstants.INVALID_PAYLOAD)
    }

    val isSenderInChat = isUserInChat(chatRoomId, senderId).bind()
    val isReceiverInChat = isUserInChat(chatRoomId, receiverId).bind()
    ensure(isSenderInChat && isReceiverInChat){
      BadRequestExceptionResponse(message = ErrorConstants.INVALID_PAYLOAD)
    }
  }

after the ensure I still see that they are nullable

score 1 · Answer 1 · answered Jul 07 '22 at 07:10

Unfortunately the compiler is not "clever enough" to know that if the check inside ensure talks about null-ness, then within the block that holds. The best solution is to use the *NotNull family of functions, some of them available at Arrow, some of them available in the standard library.

score 1 · Answer 2 · answered Jul 07 '22 at 07:15

In this case you would use ensureNotNull, which smart-casts the value to be not nullable.

suspend fun checkCanConnectDirectChat(
    senderId: Int?,
    receiverId: Int?,
    chatRoomId: Int?
  ) = either {
    ensureNotNull(chatRoomId) {
     BadRequestExceptionResponse(message = ErrorConstants.INVALID_PAYLOAD)
    }

    ensureNotNull(receiverId) {
     BadRequestExceptionResponse(message = ErrorConstants.INVALID_PAYLOAD)
    }
    val isSenderInChat = isUserInChat(chatRoomId, senderId).bind()
    val isReceiverInChat = isUserInChat(chatRoomId, receiverId).bind()
    ensure(isSenderInChat && isReceiverInChat){
      BadRequestExceptionResponse(message = ErrorConstants.INVALID_PAYLOAD)
    }
  }

An alternative is to use this: ```kotlin either { if(chatRoomId != null && receiverId != null) { shift(BadRequestExceptionResponse(message = ErrorConstants.INVALID_PAYLOAD)) } .... } ``` If only one check is wanted — Imran Malic Settuba, Jul 19 '22 at 09:51

arrow ensure doesn't make value non nullable after check

2 Answers2