Is it possible to pass null type in place of generic type parameter?

user_3581539 0
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I am going to use the following method from Spring Data Kotlin extensions:

inline fun <reified T : Any> MongoOperations.bulkOps(bulkMode: BulkMode, collectionName: String? = null): BulkOperations

The question is: can I somehow avoid specifying T assuming I do not want to provide entity class name (that's because I will explicitly specify collectionName, and in this case class type can be null). I would like to type something like:

val ops = mongoTemplate.bulkOps<null>(BulkOperations.BulkMode.UNORDERED, collectionName = "i_know_better")

Is there a type literal for null with which I can parameterize bulkOps?

kotlin generics
2 Answers

I think the short answer is no.

You seem to confuse types with values. null is a value and not a type so it cannot be used as a type in generic methods.

In your specific example, even if you could use null, looking at the code what would you expect to happen?

@Suppress("EXTENSION_SHADOWED_BY_MEMBER")
inline fun <reified T : Any> MongoOperations.bulkOps(bulkMode: BulkMode, collectionName: String? = null): BulkOperations =
        if (collectionName != null) bulkOps(bulkMode, T::class.java, collectionName)
        else bulkOps(bulkMode, T::class.java)

As you can see there's always T::class.java being called. What would be the result of null::class.java?

I'm unfamiliar with the Spring Data so I can't really provide an alternative, but I'd say you either need to search for another method or use an appropriate class here. The generic type is marked as T : Any so presumably it can be any non-nullable type. I wonder if Unit would work. Again, I'm not sure what this class is used for.

user_3444870

To answer the question in general, you can use Nothing? to represent the type that only contains the value null.

That being said, as @Fred already said, the method you're considering here explicitly states T : Any, meaning only non-nullable types are allowed. And it makes sense given that the function is accessing the class of T.

user_15408180
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