Koltin return null if value is null else-CodePudding

I work with some business logic written in Kotlin. I've got such a case in my method - I check a value for null, and if it IS null - I want to return null, else do some logic. My version looks like:

fun calculateFoo(parameter: SomeObject?): ReturnObject? = 
    if (parameter == null) null
    else performCalculation(parameter)

Literally "If value is null then return itself else process it". Normally, we do something if value is NOT null, like elvis operator, but here is "reversed" logic. Is there a better solution for this?

CodePudding user response：

You can use the ?. operator in combination with let.

fun calculateFoo(parameter: SomeObject?): ReturnObject? = 
    parameter?.let { performCalculation(it) }

CodePudding user response：

Taking a step back, if you make this an extension function with non-null parameter, it leads to more natural use at its call site.

fun SomeObject.calculateFoo(): ReturnObject = 
    performCalculation(this)


val nullable: SomeObject? = ...
val result = nullable?.calculateFoo()

I think it's better for code clarity for a function not to simply return null for a null argument, because it masks nullability at the call site, where a ?. call would suffice and keep the code clear about the possible null return value. The semantics of your function as-is allow a useless argument to be passed for a useless result.

Granted, I understand your example is contrived, and there are cases where there are multiple arguments or where a null argument only leads to a useless result under certain circumstances, in which case the ?.let answer would be more appropriate.

CodePudding user response：

Yes there is a better way to do the same,you can use this Helper class for that like this,

sealed class ResultHelper<T>(val data: T? = null, val errorMessage: String? = null) {

class Success<T>(data: T): ResultHelper<T>(data = data)

class Failure<T>(errorMessage: String): ResultHelper<T>(errorMessage = errorMessage)
}

You can also customize it according to your Use Cases.

Now you can return this class in your calculateFoo() method.

Return ResultHelper.Failure("Any error message you want to return if value is null")

Return ResultHelper.Success(ReturnObject)

From where you are accessing the returned object you can get this like this,

fun main() {
  val result = calculateFoo()
  when (result) {
   is ResultHelper.Success -> // Get Return Object like this result.data!!
   is ResultHelper.Failure -> // Handle failure, get error message like this, result.errorMessage
  }
}