How do you keep your code functionnal with nullabl...

# getting-started

[Johann Pardanaud]

How do you keep your code functionnal with nullables? For example:

val list: List<Int> = listOf(1,2,3)

list
    .firstOrNull()
    ?: -1
    .toString()
    .padStart(2, '0')

I would like to apply .toString().padStart(2, '0') to the result of list.firstOrNull() ?: -1. But, due to Kotlin's precedence, it is only applied to -1.

[Johann Pardanaud]

this is a crafted example to help comprehension, but if you want to see the real code I'm stubbling one, here it is

[Sam]

The simplest and most general answer is probably brackets:

(list.firstOrNull() ?: -1)
    .toString()
    .padStart(2, '0')

[Sam]

For a list, you can also use getOrElse(0) { ... }

[CLOVIS]

Usually, I use this as a signal that an intermediate variable would make the code clearer:

val first = list
    .firstOrNull()
    ?: -1

first.toString()
    .padStart(2, '0')

[Johann Pardanaud]

Actually, that's what I went with. I hoped there would be something a bit more chainable, but I will keep the intermediate variable 🙂

[Johann Pardanaud]

Thanks to both of you!

[Jacob]

list
.firstOrNull()
.let{it ?: -1}
.toString()
.padStart(2, '0)

[Johann Pardanaud]

oh, good idea!

[CLOVIS]

I'm not a fan. I tend to avoid using let everywhere.

[Johann Pardanaud]

In this example I find it quite readable

But I can't use it in my library code, it would be difficult to read in this case

[Youssef Shoaib [MOD]]

You can define something like:

inline fun <T: Any> T?.ifNull(replacement: () -> T) = this ?: replacement()

[Charles Flynn]

Most readable would probably be to define firstOr(X) then you have

list
    .firstOr(-1)
    .toString()
    .padStart(2, '0')

[Charles Flynn]

Lots of standard library functions have orNull() variants so as to not throw exceptions. I wonder if a more general or() version in those contexts would be useful (as well as the null version). There's always :? or other functions to deal with the null version but if ultimately you're looking for a default then it's just extra noise.