How to select a property of a struct dynamically to pass as a parameter in a function in swift 4?

Question

I am trying to lessen the number of lines in a function that I wrote. In order to achieve this I need to select a property of a struct based on some condition and pass that property as a parameter in order to compare that property among other elements in an array that are of the same struct type. Here is my gigantic code with repetition of same thing for different properties.

I have tried the following the code. Although it works as a charm but I feel the same work has been done a number of times.

func checkContentsForMatching(forIndex: Int) {
    var cards = [SetCard]()
    for index in game.indicesOfChosenCards.indices {
        cards.append(cardTitles[testCards[game.indicesofChosenCards[index]]]!)


    }

    if (cards[0].color == cards[1].color) && (cards[1].color == cards[2].color) && (cards[0].color == cards[2].color) {
        game.playingCards[game.indicesOfChosenCards[0]].color = true
        game.playingCards[game.indicesOfChosenCards[1]].color = true
        game.playingCards[game.indicesOfChosenCards[2]].color = true

    }
    else if cards[0].color == cards[1].color {
        game.playingCards[game.indicesOfChosenCards[0]].color = true
        game.playingCards[game.indicesOfChosenCards[1]].color = true

    }
    else if cards[1].color == cards[2].color {
        game.playingCards[game.indicesOfChosenCards[1]].color = true
        game.playingCards[game.indicesOfChosenCards[2]].color = true

    }
    else if cards[0].color == cards[2].color {
        game.playingCards[game.indicesOfChosenCards[0]].color = true
        game.playingCards[game.indicesOfChosenCards[2]].color = true
    }

    if (cards[0].shape == cards[1].shape) && (cards[1].shape == cards[2].shape) && (cards[0].shape == cards[2].shape) {
        game.playingCards[game.indicesOfChosenCards[0]].shape = true
        game.playingCards[game.indicesOfChosenCards[1]].shape = true
        game.playingCards[game.indicesOfChosenCards[2]].shape = true
    }
    else if cards[0].shape == cards[1].shape {
        game.playingCards[game.indicesOfChosenCards[0]].shape = true
        game.playingCards[game.indicesOfChosenCards[1]].shape = true
    }
    else if cards[1].shape == cards[2].shape {
        game.playingCards[game.indicesOfChosenCards[1]].shape = true
        game.playingCards[game.indicesOfChosenCards[2]].shape = true
    }
    else if cards[0].shape == cards[2].shape {
        game.playingCards[game.indicesOfChosenCards[0]].shape = true
        game.playingCards[game.indicesOfChosenCards[2]].shape = true
    }

Is the actual problem an implementation of Sets? If so, maybe you should ask about that and I'll show you how to implement it. As it stands, this is an x-y problem. — matt
– matt, Commented Apr 22, 2019 at 17:20
Yeah it is an implementation of Sets which was a programming assignment from CS193P. I have already implemented it. I wanted to compress my code into 300 lines if not lesser. — Rhidita
– Rhidita, Commented Apr 22, 2019 at 17:30
Yes, my implementation is quite compact (certainly a lot more compact than yours). There is a pretty elegant way to do this. — matt
– matt, Commented Apr 22, 2019 at 17:33

matt · Accepted Answer · 2022-08-21 01:31:46Z

5

What you're looking for is Swift KeyPath.

In my Sets implementation (Zotz!), this is what I do. First, I use enums with Int raw values for the four card attributes. This allows me to represent any attribute as a common type (Int). I express those raw values as computed properties, and I vend a list of all four computed properties as an array of key paths (note, this is Swift 5):

public struct Card: Codable, CustomStringConvertible {
    
    let itsColor : Color
    let itsNumber : Number
    let itsShape : Shape
    let itsFill : Fill
    
    var itsColorRaw : Int { return itsColor.rawValue }
    var itsNumberRaw : Int { return itsNumber.rawValue }
    var itsShapeRaw : Int { return itsShape.rawValue }
    var itsFillRaw : Int { return itsFill.rawValue }
    public static let attributes : [KeyPath<Card, Int>] = [
        \itsColorRaw, \itsNumberRaw, \itsShapeRaw, \itsFillRaw
    ]
    // ...
}

OK, so now the rule for whether a given triple of cards constitutes a valid match is easy to express:

private func isCorrectCards(_ cards:[Card]) -> Bool {
    func evaluateOneAttribute(_ nn:[Int]) -> Bool {
        let allSame = (nn[0] == nn[1]) && (nn[1] == nn[2])
        let allDiff = (nn[0] != nn[1]) && (nn[1] != nn[2]) && (nn[2] != nn[0])
        return allSame || allDiff
    }
    return Card.attributes.allSatisfy { att in
        evaluateOneAttribute(cards.map{$0[keyPath:att]})
    }
}

Even more elegant version suggested by @vacawama:

private func isCorrect(cards:[Card]) -> Bool {
    return Card.attributes.allSatisfy { att in
        Set(cards.map{$0[keyPath:att]}).count != 2
    }
}

edited Aug 21, 2022 at 1:31

answered Apr 22, 2019 at 17:45

matt

540k97 gold badges946 silver badges1.3k bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

matt Over a year ago

Well, you inspired me to update my code to use KeyPath and allSatisfy. My revised code has ended up even shorter and clearer than it was before!

Rhidita Over a year ago

I am like three months into coding and this my first app build in three or four days. Thank you for suggesting keypath and allsatisfy. This will surely make my code more compact.

vacawama Over a year ago

Checking for a set using Swift’s Set: Set(nn).count != 2

matt Over a year ago

@vacawama Whoa, cool! Sure, because it's 1 if they are all the same and 3 if they are all different. I can throw away evaluateOneAttribute and do the whole thing as a one-liner inside the allSatisfy block.

matt Over a year ago

Well now we're displaying both!

|

Shababb Karim · Accepted Answer · 2019-04-22 17:06:24Z

Not sure what you are trying to do but if you are trying to genericify the if-s and else-s I would do something like this:

var allColorsMatch = cards[0].color == cards[1].color) && (cards[1].color == cards[2].color) && (cards[0].color == cards[2].color

var zeroAndOneMatch = cards[0].color == cards[1].color
var oneAndTwoMatch = cards[1].color == cards[2].color
var zeroAndTwoMatch = cards[0].color == cards[2].color

game.playingCards[game.indicesOfChosenCards[0]].color = allColorsMatch || zeroAndOneMatch || zeroAndTwoMatch
game.playingCards[game.indicesOfChosenCards[1]].color = allColorsMatch || zeroAndOneMatch || oneAndTwoMatch
game.playingCards[game.indicesOfChosenCards[2]].color = allColorsMatch || zeroAndTwoMatch || oneAndTwoMatch

That's it, you don't need if-s or else-s now for color, you can replace the color if-else blocks with the code above.

Now, you might ask how would you do the same for shape. shape like color can also be true or false as far I can see. So, you might wanna wrap the above code in a function with three parameters and perform the same operations.

alexisSchreier · Accepted Answer · 2019-04-22 16:50:34Z

0

You can use Swift's higher order functions to filter your cards array instead of using a for in loop to start.

You should probably create separate model objects to avoid having to make nested subscript calls like cardTitles[testCards[game.indicesOfChosenCards[index]]]!.

Also, why is your color property in game.playingCards[game.indicesOfChosenCards[i]].color a boolean? Seems a bit confusing to have a property named color return a true of false value.

Try breaking up your function into several functions. You're trying to do too much in this one.

answered Apr 22, 2019 at 16:50

alexisSchreier

6871 gold badge5 silver badges21 bronze badges

Collectives™ on Stack Overflow

How to select a property of a struct dynamically to pass as a parameter in a function in swift 4?

3 Answers 3

6 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

6 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related