No Automatic Number Conversions

In many programming languages, you can convert numbers between shorter representations (like a Java int) and longer representations (like a Java long) just via assignments. The compiler knows to “upsize” the value.

In Kotlin, though, that only works for literals, not variables.

So, for example, as we saw earlier, this works:

  var count: Long = 5

  println(count::class)

However, this does not compile:

val thisIsInt = 5
val thisIsLong : Long = thisIsInt

println(thisIsLong::class)

The compiler error will be something akin to:

error: type mismatch: inferred type is Int but Long was expected
val thisIsLong : Long = thisIsInt

Kotlin wants you to intentionally perform such conversions. There is a toLong() function that does the trick:

  val thisIsInt = 5
  val thisIsLong : Long = thisIsInt.toLong()

  println(thisIsLong::class)