I’m asking it with no offense, just for a curiosity.
While I was coding my own org.springframework.web.method.support.HandlerMethodArgumentResolver implementation, I met a new requirement for myself, which is “Can I tell this ‘target’ parameter is Kotlin nullable?”. At a first glance, I knew that there’s org.springframework.core.MethodParameter#hasParameterAnnotation so I thought that this problem is easily solved, but what an unlucky day!
Ditched in about half hours with debugger, I finally figured out that it is impossible, because while Kotlin nullable is compiled into jvm environment, it is annotated with @org.jetbrains.annotations.Nullable but it is marked as RetentionPolicy.CLASS, on contrast to @javax.annotation.Nullable is declared as RetentionPolicy.RUNTIME.
I know that there’s a method isMarkedNullable in KType but in this scenario I only could get java.lang.Class not KClass, and during the conversion between KClass and KType, such “marked as nullable” information is completely gone because those two types are incompatible(discussed in here already).
Fortunately I found another workaround which is totally off from this topic, but still my curiosity is not resolved. Could anybody tell me some background story, reasons for this decision, etc., please?