How to create a single parameter function that can...

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[Robert Jaros]

How to create a single parameter function that can take both String or String? as a parameter and returns simple String when called with String or nullable String? when called with String??

[diesieben07]

fun <T : String?> foo(param: T): T = param

[Robert Jaros]

Is it possible to return T without unchecked cast ?

[diesieben07]

Sure, depends on what you are doing.

[Robert Jaros]

fun <T : String?> foo(str: T): T = str.toString()

[Robert Jaros]

this doesn't compile without additional cast

[diesieben07]

Well, yes, because toString always returns String, never String?

[diesieben07]

What's your use-case here? Why do you require a return-type of T, not just String?

[Robert Jaros]

Just playing with the language ;-)

[diesieben07]

In your example it makes more sense to specify a return-type of String , which is assignable to String? anyways

[Robert Jaros]

Probably yes, but it requires additional ?.let if I want to run it with nullable value

[diesieben07]

I am not sure I follow your argument

[Robert Jaros]

I'm just trying to move this check into the function

[diesieben07]

Can you show the actual code you want to replace?

[Robert Jaros]

fun <T : String?> clean(str: T): T = str?.let {
    Source(it).renderer.toString()
} as T

[Robert Jaros]

I asked my question to find out if I can do it without this as T casting

[Robert Jaros]

IntelliJ complains about it with a warning

[diesieben07]

You can write two methods:

fun clean(str: String): String = str.toString()
@JvmName("cleanNullable")
fun clean(str: String?): String? = str?.let { clean(it) }

Or, more kotlin-like, make clean an extension function and move the null-check outside:

fun String.clean() = this.toString()

// called as:
val foo: String? = TODO()
val cleaned = foo?.clean()

[diesieben07]

Personally I'd prefer the latter approach

[Robert Jaros]

Thx

[Robert Jaros]

Good idea