What is the proper way to append an element on the end of an optional array? Let's say I have an optional array, myArray, and I want to append '99' on the end. Append() does not work on a nil array, so the only solution I can find is the following, but it doesn't seem very elegant:
var myArray = [Int]?()
if myArray?.count > 0 {
myArray?.append(99)
} else {
myArray = [99]
}
You can use the fact that methods called via optional chaining always return an optional value, which is nil if it was not possible to
call the method:
if (myArray?.append(99)) == nil {
myArray = [99]
}
If myArray != nil then myArray?.append(99) appends the new element
and returns Void, so that the if-block is not executed.
If myArray == nil then myArray?.append(99) does nothing and returns
nil, so that the if-block is executed and assigns an array value.
My one liner using nil coalescing:
myArray = (myArray ?? []) + [99]
(myArray?.append(c)) ?? (myArray = [c])
@MartinR's answer is the correct answer, however, just for completeness's sake, if you have an optional and want to do different actions depending on whether it's nor or not you can just check if it's nil (or not nil):
if myArray != nil {
myArray?.append(99)
} else {
myArray = [99]
}
Note that (as you have probably figured out) optional binding doesn't work in your case because the array is a value type: it would create a copy of the array, and append a new element to it, without actually affecting the original array:
// Wrong implementation - the new item is appended to a copy of myArray
if var myArray = myArray {
myArray.append(99)
} else {
myArray = [99]
}
Instead of using append, try using array merge operator. Because the result is an optional use nil coalescing operator to assign one element array when initial array was nil.
var myArray = [Int]?()
myArray? += [99]
myArray = myArray ?? [99]
I tried to merge it into one line expression but unfortunately Swift doesn't like it
myArray = (myArray? += [99]) ?? [99]
Here’s another solution using a Swift extension:
extension Optional where Wrapped: RangeReplaceableCollection {
mutating func flatAppend(_ element: Wrapped.Element) {
if self == nil {
self = Wrapped()
}
self?.append(element)
}
}
myArray.flatAppend(99)
RangeReplaceableCollection — Array, String, ContiguousArray, etc..flatAppend(element).append(_:) on the same collection.