I'm developing a code generator that takes the data from the classes during runtime. This generator is designed to work only with Kotlin. At the moment, I was faced with the problem, as I don't know how to check if the field is nullable.
So the main question is how to implement this check via reflection?
You can check nullability with isMarkedNullable. The following code:
class MyClass(val nullable: Long?, val notNullable: MyClass)
MyClass::class.declaredMemberProperties.forEach {
println("Property $it isMarkedNullable=${it.returnType.isMarkedNullable}")
}
will print:
Property val MyClass.notNullable: stack.MyClass isMarkedNullable=false
Property val MyClass.nullable: kotlin.Long? isMarkedNullable=true
Excerpt from documentation (emphasis mine):
For Kotlin types, it means that null value is allowed to be represented by this type. In practice it means that the type was declared with a question mark at the end. For non-Kotlin types, it means the type or the symbol which was declared with this type is annotated with a runtime-retained nullability annotation such as javax.annotation.Nullable.
Note that even if
isMarkedNullableis false, values of the type can still benull. This may happen if it is a type of the type parameter with a nullable upper bound:fun <T> foo(t: T) { // isMarkedNullable == false for t's type, but t can be null here }