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?

CodePudding user response：

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.

CodePudding user response：

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.