Scala App val initialization in main method

Question

I have some code:

object Main extends App
{
    val NameTemplate = \"\"\"^([A-Za-z]+)_(\\d+)\\.png\"\"\".r

    override def main (args:Array[String])
    {
             


        

Answer 1

The DelayedInit trait (which App extends) causes rewriting of intialisation code to execute within a special delayedInit() method. This would then normally be invoked by main. Since you are overriding main, however, the delayedInit() code is never being invoked, and as such your value is not being initialised.

As @tenshi explains, you can get around this either by not extending App or by moving your main code into the body of your Main object.