When picking between a computed property versus a method in Swift, I choose a property when:

• The API I’m defining returns some form of information about an object or value’s state.
• Its body can be executed in O(1) time.

extension TodoItem {
    // Returning information about an object/value's state in
    // constant time = property.
    var isCompleted: Bool {
        return state == .completed
    }

    // Returning a new value after applying a mutation = method.
    func completed() -> TodoItem {
        var item = self
        item.state = .completed
        return item
    }

    // Returning information, but in a way that's slower than
    // constant time (O(N), where N is the number of attachments
    // in this case) = method.
    func attachmentTags() -> Set<Tag> {
        return attachments.reduce([]) { tags, attachment in
            tags.union(attachment.tags)
        }
    }
}

For two weeks, many websites around the Swift community are featuring indie developers who have been financially impacted by the current pandemic. If you can, please help support these indies by downloading their apps. Today’s app is...

HazeOver: Minimize distractions by automatically dimming all Mac windows except the currently active one. Perfect for when you want to maintain focus on a task, without having to go full screen.