Better way to deal with optional variable and array operation in Swift

Question

I have a following code, which copies an array of Rider objects, and appends a new Rider object if it exists.

let riders:[Rider] = getRiders()
let newRider:Rider? = mayGetNewRider()
var ridersPlus = riders
if let rider = newRider {
   ridersPlus.append(rider)
}

I am looking for a better (simpler and easier to read) way to write this logic, which also allows me to define ridersPlus as "let" variable.

I am looking for something like below (which is invalid, because I made up the ??? syntax, which produces an empty array of newRider is nil).

let riders:[Rider] = getRiders()
let newRider:Rider? = mayGetNewRider()
let ridersPlus = riders + [newRider???]

matt · Accepted Answer · 2018-09-18 00:34:06Z

1

How about

let ridersPlus = riders + [newRider].compactMap {$0}

(Note that before Swift 4, compactMap would be called flatMap. You didn't say what Swift version you are using.)

answered Sep 18, 2018 at 0:34

matt

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vacawama · Accepted Answer · 2018-09-18 02:21:40Z

1

You do it with map and the nil coalescing operator ??:

let ridersPlus = riders + (newRider.map {[$0]} ?? [])

map when called on an Optional value evaluates the given closure when the Optional instance is not nil, passing the unwrapped value as a parameter. If the Optional is nil, the result of the map is nil. Combining that with the nil coalescing operator, the resulting Optional array can be unwrapped or replaced with [] and then added to the riders array.

edited Sep 18, 2018 at 2:21

answered Sep 18, 2018 at 2:15

vacawama

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