Challenge 2: A reified Type Check Function — Solution

inline fun <reified T> countOfType(list: List<Any>): Int {
    return list.count { it is T }
}

fun main() {
    val mixed: List<Any> = listOf(1, "hello", 2.5, "world", 3, 4.0, "kotlin")

    println("Ints: ${countOfType<Int>(mixed)}")
    println("Strings: ${countOfType<String>(mixed)}")
    println("Doubles: ${countOfType<Double>(mixed)}")
}

/*
Output:
Ints: 2
Strings: 3
Doubles: 2

Notes:
- countOfType must be both "inline" and use "reified T" together —
  reified only works on inline functions, since the compiler needs to
  paste the function body into each call site to know the real type.
- "it is T" would be a compile error in a normal (non-reified) generic
  function, because T would be erased at runtime and unavailable to
  check against — reified is exactly what makes this check legal.
- Each call (countOfType<Int>(mixed), countOfType<String>(mixed), etc.)
  substitutes a different concrete type for T at compile time.
*/