KClass reference for nullable values

Question

In Kotlin, when declaring getting a KClass for a type, such as String::class (which represents values whose type will be String), is there a syntax to indicate that the value is nullable (ie represente String? values instead of String).

The context is that I'm trying to generate Kotlin classes using KotlinPoet but all properties I create (with PropertySpec.builder) are not nullable (String for instance, when what I actually want is String?).

Thanks for your help.

Answer 1

In case someone needs this : As of KotlinPoet 0.3.0, the syntax is :

PropertySpec.builder("myVar", String::class.asTypeName().asNullable()).mutable(true).initializer("%S", null)

to produce :

var myVar:String? = null

Answer 2

KotlinPoet 0.2.0 has just been released, and added support for nullable types, through asNullable() calls. For example:

PropertySpec.builder("name", TypeName.get(String::class).asNullable()).build()

... will create:

val name: java.lang.String?

---

Note that as the release notes mention, some function signatures in 0.2.0 have been flipped from the (type, name) order to use (name, type) order instead, so don't be scared when upgrading breaks your code.

Answer 3

No. Kotlin has Nullable types and Non-Null Types but it does not have a concept of nullable classes and non-null classes. A KType is a classifier plus nullability where a classifier can be a KClass.

KotlinPoet 0.1.0 did not have a way to represent nullable types but support for such was added in 0.2.0 via TypeName.asNullable. e.g.:

val type = TypeName.get(String::class).asNullable()

Answer 4

As for KotlinPoet 1.1.0:

Any::class.asTypeName().copy(nullable = true)

https://github.com/square/kotlinpoet#nullable-types