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iOS Generics in Swift Generic Functions, Parameters and Constraints Generic Functions with Constraints

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

Generic Functions with Constraints: Challenge

The most difficult part of this challenge was solving the function body. While it compiled correctly, I don't think it is the right implementation. An empty array does not return nil with my solution, but an array of integers does return the largest integer.

In the editor, define a function, named largest, with a generic type parameter, T. The function takes an array of type T as its first argument. Give this argument an external name of in. The return type of the function is optional T. Given an array the function should return the largest value in the array. For example, calling largest(in: [1,2,3]) should return 3. To make this work, you'll need to constrain the generic type T to conform to Comparable.

func largest<T: Comparable>(in array: [T]) -> T? {

    if array.isEmpty { return nil }

    var largest = array[0]

    for number in array {
        if number > largest {
            largest = number
        }
    }

    return largest
}

I would like to know more about creating functions, often times I find it confusing still.

8 Answers

Dan Lindsay
Dan Lindsay
39,611 Points
Dan Lindsay
Dan Lindsay
39,611 Points

Howdy,

This was my solution for that particular challenge:

func largest<T: Comparable>(in array: [T]) -> T? {
    var largest: T?

    if let largestNum = array.max() {
        largest = largestNum
    } else {
        return nil
    }

    return largest
}

Whenever I do these challenges, I setup a Playground first, then I always work to set up whatever needs to be returned, just so I don’t have to look at those red error flags. Given what the challenge asks our return type to be an Optional of type T, the first part for me was this:

func largest<T: Comparable>(in array: [T]) -> T? {
    var largest: T?

    return largest
}

From there, I did a Google search on Swift methods that return the maximum value from an array, and that is max(). Once I had that, I could create do the rest in an if let statement.

I have been able to pass all the challenges, except for the final challenge in the course(Extending Generic Types). If either of you figure that one out, let me know!

All the best!

Dan

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

Thanks Dan, I was able to refine my solution now that I see (from yours) that you can set the variable to type T?

I haven't tried the final challenge yet. I hope to get to it today.

func largest<T: Comparable>(in array: [T]) -> T? {
    var largestItem: T? = nil

    for item in array {
        if largestItem == nil {
            largestItem = item
        } else if item > largestItem! {
            largestItem = item
        }
    }
    return largestItem
}
Dhanish Gajjar
Dhanish Gajjar
20,185 Points
Dhanish Gajjar
Dhanish Gajjar
20,185 Points

Dan Lindsay Definitely your solution is the best by far! Since we didn't learn the .max() .min() properties yet I didn't try to use them.

Maria Angelica Dadalt
Maria Angelica Dadalt
6,197 Points
Maria Angelica Dadalt
Maria Angelica Dadalt
6,197 Points

Loved the way you started the challenge. The middle part is just research.

I'm going to use this method from now on!!

Neil Zimmerman
Neil Zimmerman
4,388 Points

We could use help like this everywhere. Explaining the whole process and giving examples and your reasoning is a boon for outside of this question as I still don't really understand programing yet. Examples of how to think and reason through a problem is so great.

Adam Teale
Adam Teale
10,989 Points
Adam Teale
Adam Teale
10,989 Points

Dan that's so clean! Thanks for exposing us to .max() !

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

Hi Dhanish,

Thanks for sharing. I appreciate that you are posting these since this is a new course and there isn't much guidance in the forums.

This was my solution which passed. It took me some time too since it used a few tricks that weren't part of this specific module (so probably not the best approach -- the Xcode suggestions/errors in Playgrounds eventually led me to this ).

The generics challenges have made me sweat a bit, but I am enjoying it.

func largest<T: Comparable>(in array: [T]) -> T? {
    var largestItem: Any? = nil

    for item in array {
        if largestItem == nil {
            largestItem = item
        } else if item > largestItem as! T {
            largestItem = item
        }
    }
    return largestItem as! T?
}
Dhanish Gajjar
Dhanish Gajjar
20,185 Points
Dhanish Gajjar
Dhanish Gajjar
20,185 Points

Pasan Premaratne will not be happy because you used the forced unwrap :P. I think taking it slow is a good thing, I am trying not to rush to solve the challenges. Glad you solved it though, more options help in understanding. Cheers!

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

Dhanish: good points. I refined the code above based on some new things I learned from Dan's solution (was able to get rid of the forced as! recasts) and just declare var largestItem: T? = nil. I still have a forced unwrap for item!, but this occurs after a nil check so I'm not too concerned about that :-)

The updated solution (see response to Dan) will return nil with empty array.

Dan Lindsay
Dan Lindsay
39,611 Points
Dan Lindsay
Dan Lindsay
39,611 Points

Glad this helped out! When you do get to the end of the course, please let me know if either of you find a solution for the very last challenge. I am still pretty stumped on that one. The last few videos are some concepts that I just haven't been able to grasp yet. I will come at them again tomorrow. Until then, I am working through the Java track.

Happy coding guys!

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

Dan Lindsay Have you figured out the last challenge? I'm stumped too, kind of confused with the functions, and do we extend only Array or also the Sequence protocol?

Dan Lindsay
Dan Lindsay
39,611 Points
Dan Lindsay
Dan Lindsay
39,611 Points

Hey Dhanish, I still haven't been able to solve that last challenge. Spent a couple hours on it yesterday, but nothing has clicked for me yet. Hopefully today is the day though! Let me know if you have any luck with it.

Iván Martínez
Iván Martínez
11,278 Points
Iván Martínez
Iván Martínez
11,278 Points

Here's my solution to this challenge, let me know what can i improve! :)

func largest<T: Comparable>(in array: [T]) -> T? {

    guard !array.isEmpty else {
        return nil
    }

    var largestValue = array[0]

    for item in array {
        if item > largestValue {
            largestValue = item
        }
    }

    return largestValue
}
Boris Kamp
Boris Kamp
16,660 Points
Boris Kamp
Boris Kamp
16,660 Points

I came up with this, way shorter:

func largest<T: Comparable>(in array: [T]) -> T? {
    let largest = array.max()
    return largest
}

max() is a standard swift function, so why not use this? It works on integers as wel as string arrays:

let intMax = [12, 15, 6] 
let stingMax = ["abcdefg", "abc", "abcdefghijklmnop"]
Qasa Lee
Qasa Lee
18,916 Points
Qasa Lee
Qasa Lee
18,916 Points 
func largest<T:Comparable>(in array: [T]) -> T? {
    return array.max()
}

This may help, good luck!

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

One thing I found while doing this in playgrounds is that if you don't constrain to the Comparable protocol, Xcode will give you an error saying that you have to use the max(by: ) method. This lead to me trying to figure out how to write my own comparable functionality... which for this challenge was unnecessary haha. 

func largest<T: Comparable>(in array: [T]) -> T? {
    return array.max()
}