nil value handling in Swift

Question

I am trying to build an orders array in Swift. Sometimes the values that get filled in them are nil. This leads to an app crash. Ho do I handle this?

In the code below, I loop through orders and add them to the orders array:

var orders: [order] = []
//loop
orders[i] = order(dispatchNumber: "\
(myOrder.DispatchNumber!)",orderId: "\
(myOrder.OrderId!)", source: myOrder.SourceName! , sourceAddress1: myOrder.SourceAddress! , 
    sourceAddress2: myOrder.SourceCity! + ", " + myOrder.SourceState! +
 " " + myOrder.SourceZip! , destination: myOrder.DestinationName!, 
destinationAddress1:myOrder.DestinationAddress!, destinationAddress2:
myOrder.DestinationCity! + ", " + myOrder.DestinationState! + " " +
 myOrder.DestinationZip! , loads: "\(myOrder.LoadCount!)",
 loadsDelivered: "\(myOrder.LoadsDelivered!)",  tons: "\

(myOrder.TonsCount!)", price: "$" + "\(myOrder.PayRate!)", sourceDistance: myOrder.DistanceToSource!, onewayDistance: myOrder.OrderLegDistance!,  pickupStart: myOrder.PickupBy!, earliestDelivery: myOrder.DeliverStart!,latestDelivery: myOrder.DeliverBy!,product: myOrder.ProductName! , loadsRemaining: "\(thisLoadsRemaining)", truckType: myOrder.TruckType!, notes:
 myOrder.Notes!, isStarted: myOrder.IsStarted, isOnHold: myOrder.IsOnHold, payRateType: "\(myOrder.PayRateType!)", 
isStayOn: myOrder.IsStayOn, customerName: myOrder.CustomerName! )

Sometimes myOrder.OrderLegDistance! gets a nil value. How do I handle it?

Read something like https://stackoverflow.com/questions/24003642/what-is-an-optional-value-in-swift#24026093 — David Neiss, Sep 28 '17 at 16:14
Easy way to not crash: don't use the `!` operator. How do you *want* to handle it? — Ssswift, Sep 28 '17 at 16:52
I checked for the nil value i.e. var orderLegDistance = "--" if myOrder.OrderLegDistance != nil { orderLegDistance = myOrder.OrderLegDistance! } — Ackman, Sep 28 '17 at 17:07

score 3 · Answer 1 · answered Sep 28 '17 at 16:14

It's generally a bad idea to use implicitly unwrapping. Always handle the values safely.

Use guard let or if let to make sure the variables have a value when you work with them.

if let distance = orderLegDistance {
    print("\(distance)")
}

guard let distance = orderLegDistance else {
    print("Error: distance is empty")

    return
}

Moreover, you can define a default value by using ??.

print("\(orderLegDistance ?? 0)") /*this will print 0 if orderLegDistance is empty*/

On a side note, always use camelCase variable names instead of PascalCase.

Thanks Appreciate the help :) – Ackman Sep 28 '17 at 17:06 — Ackman, Sep 28 '17 at 17:06

score 1 · Answer 2 · answered Sep 28 '17 at 16:14

1

Depends of your business rules :

If the OrderLegDistant is a mandatory value, you may want to 'forget' this order. In order to do that you can use a guard statement, to check all the mandatory params.
If theOrderLegDistant is not mandatory, update your model to have this attribute as Optional, and remove the unwrap (!) from your constructor.

answered Sep 28 '17 at 16:14

CZ54

5,488
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Thanks Appreciate the help :) – Ackman Sep 28 '17 at 17:06

CSjunkie · Accepted Answer · 2020-01-09T15:13:06.417

1

The safe bet would be to check for nil before unwrapping.

var orderLegDistance = defaultValue if myOrder.OrderLegDistance != nil { orderLegDistance = myOrder.OrderLegDistance! }

You can use the same kind of check to determine that you need to ignore the value of myOrderLegDistance if your logic demands that.

EDIT Adding some additional unwrapping options here:

if let legDistance = myOrder.OrderLegDistance {
    orderLegDistance = legDistance
}

Or, as mentioned in a comment below:

orderLegDistance = myOrder.OrderLegDistance ?? defaultValue

edited Jan 09 '20 at 15:13

answered Sep 28 '17 at 16:43

CSjunkie

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You could achieve the same with `var orderLegDistance = myOrder.OrderLeftDistance ?? defaultValue`. – zneak Sep 28 '17 at 16:49

nil value handling in Swift

3 Answers3