does anybody know how to get the type (KType / KClass ?) of the embedded value in a value class? ```...

# announcements

[Peter Ertl]

does anybody know how to get the type (KType / KClass ?) of the embedded value in a value class?

if (klass.isValueClass) {
  // TODO get type of embedded value for further processing
}

update - I think I found it:

if (klass.isValue) {
  val ctor = klass.primaryConstructor ?: error("value class has no primary constructor")
  val valueType = ctor.parameters.firstOrNull()?.type ?: error("value class has no single parameter in constructor")
   // use it
}

If somebody knows a shorter way I would appreciate

[ephemient]

kotlin value classes are planned to allow any number of fields, going along with project valhalla in jvm

[ephemient]

https://youtrack.jetbrains.com/issue/KT-1179 actually it seems there's a plan to enable that even without valhalla

[Peter Ertl]

ah ok - good to know. Is @JvmInline an indication that only a single parameter is allowed?

[Peter Ertl]

since I am writing on an typescript generator to map inline classes correctly

[ephemient]

https://github.com/Kotlin/KEEP/blob/master/notes/value-classes.md#multifield-value-classes-before-valhalla

In fact, there are legitimate use-cases for “inlined” multi-field value classes support on pre-Valhalla JVM. Consider the following example:

@JvmInline
value class Complex(val re: Double, val im: Double)

[ephemient]

so right now, all value classes are single-parameter, but with or without @JvmInline that restriction will probably disappear

[Peter Ertl]

thanks a lot @ephemient

[Peter Ertl]

i really appreciate

[Peter Ertl]

🙂

[Peter Ertl]

so if I get it right value classes vs. regular classes are all about controlling whether to use heap or stack allocated memory?

[ephemient]

not how I would put it... it's about object identity.

[ephemient]

"is there any distinction between InlineClass(1) constructed here versus InlineClass(1) constructed there"

[ephemient]

if the answer is no, then it enables a number of further optimizations... but it's not really about stack vs heap, JVM will box value classes onto the heap in plenty of situations, K/N can place regular classes on the stack as long as escape analysis works...

[Peter Ertl]

wow, that makes it a lot clearer on what all it is about … thanks for sharing your knowledge 👍😎