Ytukyg

IntelliJ gives the following complaint:

Lambda argument should be moved out of parentheses

val profile = loadProfiles()

profile.sortedWith(Comparator({ profile1, profile2 ->

                if (profile1.age > profile2.age) return@Comparator 1

                if (profile1.age < profile2.age) return@Comparator -1

                return@Comparator 0

            }))



data class Developer(var age: Int)



fun loadProfiles(): List<Developer> {

    val listOfNumber = listOf<Developer>(Developer(2), Developer(5), Developer(3))



    return listOfNumber

}

How should I format the above to get rid of the complaint? Also, the sorting code doesn't sort. What is causing the problem?

sortedWith(): Returns a list of all elements sorted according to the
specified [comparator]

So to sort profile list you have to assign the list returned by sortedWith() to profile (also change its declaration from val to var)

var profile = loadProfiles()

profile = profile.sortedWith(Comparator { profile1, profile2 ->

    if (profile1.age > profile2.age) return@Comparator 1

    if (profile1.age < profile2.age) return@Comparator -1

    return@Comparator 0

})



profile.forEach { println(it.age) }

or

val profile = loadProfiles().sortedWith(Comparator { profile1, profile2 ->

    if (profile1.age > profile2.age) return@Comparator 1

    if (profile1.age < profile2.age) return@Comparator -1

    return@Comparator 0

})

For the warning: press Alt+Enter and let InteliJ make the change.

This warning is caused because in Kotlin labda parameters can (and actually should be) outside parentheses.

See this:

fun onClick(action: () -> Unit) { ... }

When you use function like this you can use:

view.onClick({ toast(it.toString())} )

view.onClick() { toast(it.toString()) }

view.onClick { toast(it.toString()) }

All of those forms are correct (compiler will not fail), but in Kotlin Style Guide you'll find following statement:

If a call takes a single lambda, it should be passed outside of
parentheses whenever possible.

@see https://kotlinlang.org/docs/reference/coding-conventions.html#lambda-formatting

That's why IntellJ shows warning. You can click alt + enter and IntellJ should show correct solution, or just move lambda out of parentheses. And if labda is only argument remove parentheses also.
When lambda have to be in parentheses? Only when it is not last parameter in function.

As for your immediate problem, you just have to write it like this:

profile.sortedWith(Comparator { profile1, profile2 ->

            if (profile1.age > profile2.age) return@Comparator 1

            if (profile1.age < profile2.age) return@Comparator -1

            return@Comparator 0

        }

)

However, the code still has several layers of unneeded verbosity. Here are some ways to make it both more concise and more readable.

1. 
   

   Remove the return statement:

   
   
   

   profile.sortedWith(Comparator { profile1, profile2 ->
   
       if (profile1.age > profile2.age) 1
   
       else if (profile1.age < profile2.age) -1
   
       else 0
   
   })
   
   

   
   


2. 
   

   Use when instead of an if-else cascade:

   
   
   

   profile.sortedWith(Comparator { profile1, profile2 ->
   
       when {
   
           profile1.age > profile2.age -> 1
   
           profile1.age < profile2.age -> -1
   
           else -> 0
   
       }
   
   })
   
   

   
   


3. 
   

   use Int.compareTo:

   
   
   

   profile.sortedWith(Comparator { profile1, profile2 ->
   
       profile1.age.compareTo(profile2.age) 
   
   }
   
   

   
   


4. 
   

   use compareBy:

   
   
   

   profile.sortedWith(compareBy(Profile::age))
   
   

   
   


5. 
   

   Don't use the general sortedWith when all you need is sortedBy:

   
   
   

   profile.sortedBy(Profile::age)