```val foo String = null bar foo fun bar value Any when valu kotlinlang #announcements

val foo : String? = null

bar(foo)

fun bar(value: Any?){
    when(value){
        is Int? -> println("Int?") // always prints Int? when value == null
        is String? -> println("String?")
    }
}

Is there any way to get the actual type of

value

Shawn

02/01/2020, 8:38 PM

Well, I know of a technique that would approximate what you’re looking for, but it’s important to note that

null

has no type (sort of), and the type system can’t resolve magical intent here at runtime

what you’re looking for probably looks something more like this:

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inline fun <reified T : Any> bar(value: T?) {
  when (T::class) {
    Int::class -> println("Int?")
    String::class -> println("String?")
  }
}
bar(foo)  // String?

you can use type inference to keep the call site looking clean and use

reified

to do the dirty work

Lawik

02/01/2020, 8:52 PM

Thanks!

Wait this doesn't solve my problem. I am actually passing

vararg

to my function and it doesn't work in that case 😔

I am trying to achieve a helper function for JDBC which will take a number of arguments and set the parameter of the prepared statement for each argument.

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fun PreparedStatement.setParams(vararg params: Any?) {
    params.forEachIndexed { index, param ->
        val paramIndex = index + 1
        when (param) {
            is String -> this[paramIndex] = param
            is String? -> this[paramIndex] = param
            is Int -> this[paramIndex] = param
            is Int? -> this[paramIndex] = param
            is Short -> this[paramIndex] = param
            is Short? -> this[paramIndex] = param
            is Byte -> this[paramIndex] = param
            is Byte? -> this[paramIndex] = param
            is Long -> this[paramIndex] = param
            is Long? -> this[paramIndex] = param
            is Boolean -> this[paramIndex] = param
        }
    }
}

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operator fun PreparedStatement.set(index: Int, value: String?) {
    if (value != null) {
        this.setString(index, value)
    } else {
        this.setNull(index, Types.VARCHAR)
    }
}

// ... other PreparedStatement.set(..) functions

diesieben07

02/01/2020, 9:27 PM

There is no way for the compiler to know if you want a nullable string or a nullable int if all you give it is

null

👆 1

nkiesel

02/03/2020, 9:29 PM

or you could just call

setObject

and let the JDBC driver/DB sort this out for you

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