Using the where keyword can be a super nice way to quickly apply a filter in a for-loop in Swift. You can of course use map, filter and forEach, or guard, but for simple loops I think this is very expressive and nice.

func archiveMarkedPosts() {
    for post in posts where post.isMarked {
        archive(post)
    }
}

func healAllies() {
    for player in players where player.isAllied(to: currentPlayer) {
        player.heal()
    }
}