Why does Kotlin's compiler not realize when a variable is initialized in an if statement?-CodePudding

The following example of Kotlin source code returns an error when compiled:


fun main() {

  var index: Int // create an integer used to call an index of an array
  val myArray = Array(5) {i -> i   1} // create an array to call from

  val condition = true // makes an if statement run true later

  if (condition) {
    index = 2 // sets index to 2
  }
    
  println( myArray[index] ) // should print 2; errors
  
}

The error says that the example did not initialize the variable index by the time it is called, even though it is guaranteed to initialize within the if statement. I understand that this problem is easily solved by initializing index to anything before the if statement, but why does the compiler not initialize it? I also understand that Kotlin is still in beta; is this a bug, or is it intentional? Finally, I am using Replit as an online IDE; is there a chance that the compiler on the website simply is an outdated compiler?

CodePudding user response：

The compiler checks whether there is a path in your code that the index may not be initialized based on all the path available in your code apart from the value of the parameters. You have an if statement without any else. If you add the else statement you will not get any compile error.