How to create an extension on Swift Array to replace nil with a value?-CodePudding

I tried the following but I continued to get an array of optionals even though I am using compactMap.

let numbers: [Int?] = [2, 4, 5, nil, 8]

extension Array where Element: Equatable {
    func replaceNil(with element: Element) -> [Element] {
        self.compactMap { $0 == nil ? element : $0 }
    }
}
print(numbers.replaceNil(with: 0))

CodePudding user response：

The use of compactMap is incorrect here. compactMap turns a [T] to another [U] - it is the mapping function that is allowed to return an optional ((T) -> U?), and it removes any element for which this function returns nil. This property can be used to remove nils from a [T?] and get a [T] by passing it { $0 }, but that's not what you are trying to do with the [T?] in this case.

What you want here is to turn a [T?] to [T], and you have a one-to-one mapping, which can be done with a map like this:

extension Sequence {
    func replacingNil<T>(with element: T) -> [T] where Element == T? {
        self.map { $0 ?? element }
    }
}