Swift How could I safely unwrap an optional property when filtering an array?

Question

I am trying to filter an array of objects with an optional property of the objects' class, so I was wondering what's the best way to unwrap this property safely without providing a default value. The property is of type Date so providing an alternative value feels like a hack, but I'm not sure how to do it better. I know how to safely unwrap a regular optional with guard but I'm not sure how to use this when filtering an array. The code I have is this:

let completedGoalsThisWeek = goals.filter { $0.returnWeek(date: $0.dateAchieved) == deviceWeek }.count

The property in question is dateAchieved and it will be nil in a lot of circumstances.

Thank you.

Answer 1

There's nothing special to it. Just unwrap the optional like you would in any other case:

let completedGoalsThisWeek = goals
    .lazy
    .filter { goal -> Bool in
        guard let dateAchieved = goal.dateAchieved else { return false }
        let isCurrentWeek = goal.returnWeek(date: dateAchieved) == deviceWeek
        return isCurrentWeek
    }.count

You could use Optional.map to shorten this, but I would advise against it, it's too cryptic:

let completedGoalsThisWeek = goals
    .lazy
    .filter { goal
        goal.dateAchieved.map { goal.returnWeek(date: $0) == deviceWeek } ?? false
    }.count

In either case, I suggest you use .lazy.filter, to prevent the intermediate allocation to hold an array of elements, if you're ultimately going to only count them and immediately discard them.