Adding Protocol Conformance with an Extension

Using Swift
1

protocol RandomNumberGenerator {
func random() -> Double
}

class Dice {
let sides: Int

let generator: RandomNumberGenerator

init(sides: Int, generator: RandomNumberGenerator) {

self.sides = sides

self.generator = generator
}

func roll() -> Int {
return** Int(generator.random() * Double(sides)) + 1
}
}

class LinearCongruentialGenerator: RandomNumberGenerator {

var lastRandom = 42.0

let m = 139968.0

let a = 3877.0

let c = 29573.0

func random() -> Double {

lastRandom = ((lastRandom * a + c).truncatingRemainder(dividingBy: m))

return lastRandom / m

}
}

//You can extend an existing type to adopt and conform to a new protocol
protocol TextRepresentable {
var textualDescription: String { get }

}

//The Dice class from above can be extended to adopt and conform to TextRepresentable:

extension Dice: TextRepresentable { // here is the issue, TextRepresentable //is ambiguous for type lookup in this context

var textualDescription: String {

return "A (sides)-sided dice"
}
}

let d12 = Dice(sides: 12, generator: LinearCongruentialGenerator())

print(d12.textualDescription)

//must Prints "A 12-sided dice"

2

Hello and welcome to the forums, @Hossam!

It would probably be helpful if you edited and formatted your question so that the source code is easier to read. If you're unfamiliar with markdown there's a GUI for it right above the edit field, just put your source code snippets inside a "Preformatted text" block (the </> symbol).
You have to provide indents to make it more readable then, too.

That being said, I don't really know what you mean with your question. On first glance and a quick copy&paste to a playground above code seems fine. Conforming to a protocol via an extension like is totally fine.

Update: I just noticed that your one protocol is called RandomNumberGenerator, be aware that the standard library also contains a protocol with that name. That seems unrelated to your question, though? (If you have need for both you can still reference the standard library's one via Swift.RandomNumberGenerator, btw).

3

Thanks for replying,
the issue is that (see this code below , is not running because TextRepresentable is ambiguous )

extension Dice: TextRepresentable { // here is the issue
var textualDescription: String {
return "A (sides)-sided dice"
}
}

4

If you put your code between ``` ticks like these:

```
extension Dice { ... }
```

It will look like this:

extension Dice { ... }
5

Please format your code as @sveinhal explains (which I should have done as well in the first place... :smiley:).

I understood that you meant to indicate you see a problem in that line, but whatever causes the warning/error in your codebase is not part of what you posted.

Allow me to post a commented, formatted, and slightly rearranged version of youd code:

// MARK: - The protocols
protocol RandomNumberGenerator {
    func random() -> Double
}

protocol TextRepresentable {
    var textualDescription: String { get }
}

// MARK: - The classes
class Dice {
    let sides: Int
    let generator: RandomNumberGenerator

    init(sides: Int, generator: RandomNumberGenerator) {
        self.sides = sides
        self.generator = generator
    }

    func roll() -> Int {
        return Int(generator.random() * Double(sides)) + 1
    }
}

class LinearCongruentialGenerator: RandomNumberGenerator {
    var lastRandom = 42.0
    let m = 139968.0
    let a = 3877.0
    let c = 29573.0

    func random() -> Double {
        lastRandom = ((lastRandom * a + c).truncatingRemainder(dividingBy: m))
        return lastRandom / m
    }
}

// MARK: - Making Dice adopt TextRepresentable in an extension
extension Dice: TextRepresentable { // this totally compiles
    var textualDescription: String {
        return "A \(sides)-sided dice"
    }
}

let d12 = Dice(sides: 12, generator: LinearCongruentialGenerator())
print(d12.textualDescription) // this prints as expected

I don't get what would cause a "TextRepresentable is ambiguous for type lookup in this context" warning/error, in fact I have not seen that one before myself.

You can check yourself by copying & pasting this into a fresh, empty playground (I am using Xcode 14.0.1, so Swift 5.7) and let it run, it works. I have no idea what causes your warning/error without more context.

1 Like
6

it running now, thank you very much ,
i don't know why was not running but after i copied you code it runs straight away.

7

Nice, glad it now works (though it would be interesting to know what caused this). For what it's worth: There was one typo in your original code that I simply omitted as it seemed unrelated: In your Dice's roll() method there were two ** after your return statement, but that just has the compiler error on that line and has nothing to do with TextRepresentable. I assumed that just came to be when posting your code as the post has, as stated, some weird/lacking formatting in the first place. :slight_smile:

Have fun coding, and again, welcome to the forums!

1 Like