Swift method which returns array

Question

So, I have a question about how my class and struct interfaces should look like in Swift. For example I have a class or struct which has method:

func getAllObjectsFromSomewhere() -> [Int]

but, imagine that this method not always return you some array of Int, so there are few different ways how to handle it.

func getAllObjectsFromSomewhere() -> [Int]?
func getAllObjectsFromSomewhere() throws -> [Int] Throws custom ErrorType with types like: NotFound or EmptyArray
func getAllObjectsFromSomewhere() -> [Int] { /* some code and then just return an empty Int array */ return [Int]() }

So, my question is, when and why I should take which approach of organising the interface? Does it make much difference? Is there any guidelines?

Do you have a specific use case or more details about this method? Or is this purely hypothetical? — Ryan Poolos
– Ryan Poolos, Commented Sep 6, 2016 at 13:10
@RyanPoolos I faced this during building architecture for one of my apps, but I think I want the most common answer, so yes, this is purely hypothetical. — Pavel Gatilov
– Pavel Gatilov, Commented Sep 6, 2016 at 13:11

Sergey Kalinichenko · Accepted Answer · 2016-09-06 13:12:36Z

2

All three approaches are valid, depending on a situation:

When getting objects may or may not be possible, and impossibility does not necessarily mean an error, use [Int]?. This lets you differentiate between an empty array and no array at all.
When getting objects must always be possible, and impossibility to get them means you have an error, use throws
When inability to get objects should always be treated as an absence of objects, use [Int] and an empty array.

answered Sep 6, 2016 at 13:12

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

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

4 Comments

Pavel Gatilov Over a year ago

That is what was in my mind, but, I am not quite sure about application. For example, I am trying to get a list of objects from some abstract database. Which one I should use? Does it depends on which level of architecture I want to get this?

Pavel Gatilov Over a year ago

Because, for example, if it is low level model, I want to deal with throws, if it is something close to view, like viewModel, I don't want to deal even with nil values.

Pavel Gatilov Over a year ago

And one more time for example, if I executed request to database, and I got 0 results, should I return empty array? or nil?

Sergey Kalinichenko Over a year ago

@PavelGatilov When DB request returns successfully with zero rows, this means that there are no rows, but they could be there. Hence, you should return an empty array. Returning nil or throwing an exception should be an option only when there is an error with the request. You should always throw if the request itself is invalid due to a programming error.

Community · Accepted Answer · 2020-06-20 09:12:55Z

This is just my opinion and I don't have any guidelines or anything to throw behind it, but...

Straight out of the box I think this is a perfect case for optionals, meaning this signature:

func getAllObjectsFromSomewhere() -> [Int]?

But (as always :)) it depends on the situation. Here are my thoughts on your scenarios.

func getAllObjectsFromSomewhere() -> [Int]?

This is what I'd normally use if I was to implement that function.

You have a normal case where you expect to get some Ints returned in an array.

If for some reason there are no elements, then you get a nil in return which you can then check for using a guard or an if let.

Normally, an empty array should't be enough reason to actually start throwing exceptions, but it depends on the specific case of course.

func getAllObjectsFromSomewhere() throws -> [Int]

If however, you actually expect that your getAllObjectsFromSomewhere must return a value, then it would make sense to throw an error if for some reason there wasn't any content to return.

func getAllObjectsFromSomewhere() -> [Int]

This is the solution I like the least.

When you call your getAllObjectsFromSomewhere you still need to do a check and see if the returned array actually contains anything (if getAllObjectsFromSomewhere().count > 0) before you decide what to do....why not use guard or if let for that?

As said, this was just my thoughts on the three scenarios, hope you can use them.

Collectives™ on Stack Overflow

Swift method which returns array

2 Answers 2

4 Comments

func getAllObjectsFromSomewhere() -> [Int]?

func getAllObjectsFromSomewhere() throws -> [Int]

func getAllObjectsFromSomewhere() -> [Int]

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

func getAllObjectsFromSomewhere() -> [Int]?

func getAllObjectsFromSomewhere() throws -> [Int]

func getAllObjectsFromSomewhere() -> [Int]

Comments

Your Answer

Sign up or log in

Post as a guest

Related