Hi Guys is there a more clean kotlin way to write this code

Question

Hi Guys is there a more clean kotlin way to write this code ``` if v1 == null amp amp v2 == null return 0 if v1 = null amp amp v2 == null return 1 if v1 == null amp amp v2 = null return 1 ```

diesieben07 · Answer

arturro Is that in a Comparator

arturro · Answer

yes

arturro · Answer

It looks like this ``` override fun compare o1 T o2 T Int val property = o1 javaClass kotlin declaredMemberProperties first it gt it name == propertyName val v1 = property get o1 as Comparable lt Any gt val v2 = property get o2 as Comparable lt Any gt if v1 == null amp amp v2 == null return 0 if v1 = null amp amp v2 == null return 1 if v1 == null amp amp v2 = null return 1 return v1 compareTo v2 ```

diesieben07 · Answer

You could just do `val c = compareBy MyClass property `

arturro · Answer

I dont know the property

arturro · Answer

I know it only at runtime as a string name

diesieben07 · Answer

Then you look it up using reflection and then pass it to `compareBy`

diesieben07 · Answer

And then you can use `nullsLast` resp `nullsFirst` to allow nulls

arturro · Answer

I am not sure how to do this Now I have ``` fun lt T Any gt List lt T gt sortByProperty propertyName String asc Boolean = true List lt T gt val field = return this sortedBy field ``` But it does n compile

diesieben07 · Answer

`T` would have to be reified so you can get it s class Then you can use T class to look up the property

diesieben07 · Answer

`propertyName` should really not be a string though

cedric · Answer

Do not use reflection in a comparator

arturro · Answer

I have to slightly smiling face

cedric · Answer

Then at least don t do so for every call of `compare`

arturro · Answer

Now I have something like this ``` inline fun lt reified T Any gt List lt T gt sortByPropertyName propertyName String List lt T gt val prop = T class declaredMemberProperties first it name == propertyName return this sortedBy prop ``` But it doesn t compile the error is ``` Error 11 17 Kotlin Type parameter bound for R in inline fun lt T R Comparable lt R gt gt Iterable lt T gt sortedBy crossinline selector T gt R List lt T gt is not satisfied inferred type KProperty1 lt T gt is not a subtype of Comparable lt KProperty1 lt T gt gt ```

arturro · Answer

Any suggestion how to fix it are welcome slightly smiling face

cedric · Answer

< artur> `prop` itself does not implement `Comparable` you need code in there that can be mapped by the compiler to a `Comparable`

cedric · Answer

e g ` return this sortedBy 1 ` obviously not what you want but you get the idea

artur · Answer

Thks Cédric