Unwrap an Array of Optional Values Using Swift

If we aren't interested in nil

Keywords and Terminology

Array: an ordered series of objects which are the same type (article) compactMap: Returns an array containing the non-nil results of calling the given transformation with each element of this sequence Force unwrapping: A method in which an optional is forced to return a concrete value. If the optional is nil, this will cause a crash Optionals: Swift introduced optionals that handle the absence of a value, simply by declaring if there is a value or not. An optional is a type on it's own! (article)

The opportunity

In this example there is an Array of Strings and nil, that is an array of optionals because some of the values are Strings and some are represented by nil.

This is all fine - but what if you want to do something to each of these Strings using something like Mapping where we run the same function against every element in the array. This can be written as:

let uppercaseArray = arrayOfOptionals.map{ $0?.uppercased() }

Now I'm not a big fan of the optional question mark ?, and the reason for that becomes apparent when we print out this array to the console (by running print(uppercaseArray)):

Oh my word! What a mess when printed to the console! What if I needed to present this data to the end user? This would be awful, right?

Ignore nil with compactMap

We don't care about those nil values in this example, effectively we want rid of them. In order to do this we can use compactMap

Zap those optionals

The optionals can be eradicated from the array with compactMap with something like

let arrayWithNoOptionals: [String] = arrayOfOptionals.compactMap { $0 }

I have explicitly detailed the type here, but this can be removed when writing Swift (although it is a little less clear what the resulting array type is):

let arrayWithNoOptionals = arrayOfOptionals.compactMap { $0 }

Which gives us an array of (if we print out the resultant array with something like print(arrayWithNoOptionals)):

["There", "Present", "Not nil", "Some"]

which can then be used along with uppercase to only write those values in capital letters

let uppercased = arrayWithNoOptionals.map{ $0.uppercased() }

Which we can the write to the console (again, something like print(uppercased)). Which gives the expected result of:

["THERE", "PRESENT", "NOT NIL", "SOME"]

What's more, you know what - this could all be done in a single line. That's detailed in the video though!

Conclusion

I hope you enjoyed that rather short article. Please do keep a look out for me, if you are interested in such articles in the future! Thank you! Oh, and keep an eye out for articles on mapping, perhaps this one - it might give you a good view of how mapping and compactMap might work in context. If you've any questions, comments or suggestions please hit me up on Twitter