Is there a way to know information of collection? ...

# reflect

[kennyyi]

Is there a way to know information of collection?

fun foo(clazz: Class<*>) {
  // 1. How to know clazz is collection?
  // 2. How to know T of Collection<T> is String?
}

fun myFunc() {
  val mySet: HashSet<String> = HashSet()
  foo(mySet::class.java)
}

[diesieben07]

No. At runtime HashSet<String> and HashSet<Foo> are represented by the same (erased) class HashSet.
You can do some clever tricks with subclasses and the reified keyword, but your example is not possible.

[kennyyi]

Thanks, I solved this issue with making annotation.

for example,

annotation class ElementType(val element: KClass<*>)

...

@ElementType(String::class)
class Names: HashSet<String>()

...

foo() {
    ...
    val elementType = clazz.annotations.find{ it is ElementType }
    elementType?.let {
        val elementClass = (elementType as ElementType).element
        ...
    }
    ...
}