Ch. 21, Generics, Gold Challenge

Swift Programming (3rd Edition) 21. Generics
1 
   func findAll<T: Collection, U: Equatable>(_ collection: T, _ item: U) -> [Int] where T.Element == U {
      var findedIndexes = [Int]()
      
        for (index, element) in collection.enumerated() {
            if element == item {
                  findedIndexes.append(index)
            }
        }
        return findedIndexes
    }
2

Your code looks prettier if you enclose it with a pair of three back-tick characters (```) like this: :slight_smile:
```
Code
```

func findAll <T: Collection, U: Equatable> (_ collection: T, _ item: U) -> [Int] where T.Element == U {
  var foundIndexes = [Int]()
  
    for (index, element) in collection.enumerated () {
        if element == item {
           foundIndexes.append (index)
        }
    }
    return foundIndexes
}
1 Like
3

Thanx! :slight_smile:

4

Hi @mgmzlm,
I saw that you use enumerated method from Collection protocol.
How do you hear about this method?

Good bye!

5

I read Apple documentation on Collection and Sequence.

6

The developer documentation from Xcode or from the website?

7

They are same in content.

8

Ok :upside_down_face:

1 Like
9

How do you hear about this method?

10

I read Apple documentation on Collection and Sequence.

11

Here’s my solution for the Gold Challenge

func findAll<C: Collection, T: Equatable>(_ collection: C, _ element: T) -> some Collection {
    var positions = [T]()
    for (i, item) in collection.enumerated() where item as! T == element {
        positions.append(i as! T)
    }
    return positions
}

findAll([5,3,7,3,9], 3)    //[1, 3]

However, I’m not sure if I satisfied the requirements to change the return type from [Int] to an array of an associated type of the Collection Protocol. Can someone give me some feedback?

12

I tried a slightly different solution that dealt with the question of changing the return type:

func findAll<T: Equatable, S: Collection>(_ collection: S, _ element: T) -> [S.Index] where S.Element == T {
    var indexes = [S.Index]()
    
    var i = collection.startIndex

    while i != collection.endIndex {
        if collection[i] == element {
            indexes.append(i)
        }
        i = collection.index(after: i)
    }

    return indexes
}

var strArray = findAll("StringTest", "t")    // [{_rawBits 65793}, {_rawBits 590081}]
print("StringTest"[strArray[0]])             // t

let str2 = ["A", "AB", "ABC", "A"]
print(findAll(str2, "A"))                   // [0, 3]