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iOS Generics in Swift Generic Functions, Parameters and Constraints CSS Background Blend Modes Challenge

Dhanish Gajjar
Dhanish Gajjar
20,185 Points
Posted by Dhanish Gajjar
Dhanish Gajjar
20,185 Points

Generics in Swift 3, Challenge 2

I tried a lot of different ideas. I also created a simple square function. But somehow I ended up with a square function that takes an array of Int and returns an array of Int.

But I think that is not correct. Can anyone guide me here.

In the editor define a function named map with two generic type parameters, T and U. The function takes two arguments - array of type [T], and transformation of type (T) -> U. The function returns an array of type U. The goal of the function is to apply the transformation operation on the array passed in as argument to return a new array containing the values transformed. For example given the array [1,2,3,4,5] as first argument, and a square function as the transformation argument, the result should be [1, 4, 9, 16, 25].

Thank you!

generics.swift 
func map<T, U>(array: [T], transformation: (T) -> U) -> U {

}
Dhanish Gajjar
Dhanish Gajjar
20,185 Points
Dhanish Gajjar
Dhanish Gajjar
20,185 Points 
func map<T, U>(array: [T], transformation: (T) -> U) -> [U] {
    var results = [U]()

    for i in array {
        let value = transformation(i)
        results.append(value)
    }

    return results
}

func squareOf(_ number: Int) -> Int {

    let square = number * number

    return square
}

Figured out! .... Phew!

David Papandrew
David Papandrew
8,386 Points
David Papandrew
David Papandrew
8,386 Points

Hi Dhanish, thanks for posting this. I was having trouble with this challenge too. I was trying to do the same thing as you (function that takes a generic array and returns a squared array). Your post clarified things for me when I realized I just needed to take a single value and return a single value. It should have been clear from the function signature, but I think the challenge could have provided a little more guidance on this matter!

2 Answers

Dhanish Gajjar
Dhanish Gajjar
20,185 Points
Dhanish Gajjar
Dhanish Gajjar
20,185 Points

David Papandrew I am glad it helped and you're right, it is a bit confusing, because the challenge explicitly mentions it accepts an array of type [T] , transformation of (T) -> U and the entire function returns an array of type U.

We immediately think that U represents an array, which means transformation also accepts an Int and returns an array. I went back and forth and it took time, but it compiled in the end.

I still don't know if this was the right thing to do, I am waiting on others to give their opinion here :)

Stephen Wall
PLUS
Stephen Wall
Courses Plus Student 27,294 Points
Stephen Wall
Stephen Wall
Courses Plus Student 27,294 Points

Looks like you already have a working answer but I found a cool little trick for iterating through the [T] array and appending to the [U] array.

func map<T, U>(array: [T], transformation: (T) -> U) -> [U] {
    let results: [U] = []
    array.forEach { item in
        results.append(transformation(item))
    }
    return results
}