random-data-generator | Random generator of test data | Testing library

The random generator depends on an implicit value of type ClassTag to do its thing. However, A is not known until another trait or class actually extends Foo, so the compiler cannot provide the implicit parameter like it did with fooBound. Try keeping 'a' abstract and then overriding it in other classes, or passing A in as a ClassTag maybe? Look at the source code here to see https://github.com/DanielaSfregola/random-data-generator/blob/master/js/src/main/scala/com/danielasfregola/randomdatagenerator/RandomDataGenerator.scala

Casting changes the compile-time type, not the runtime type. Pattern matching checks the runtime type. In fact, case class pattern matching even has an explicit check for null; see Why is there a `null` check in the implementation of the `unapply` method for case classes? (though that check doesn't affect your case since you're using a type pattern).

Also, even if it weren't for the pattern matching issue, you wouldn't be able to "operate on the class's fields" without getting a NullPointerException.

Since there are three ranges of 0 to 255, each represented with max of 0xff and they all are concatenated in a single value, we can directly take a random value in the range of 0... 0xffffff and produce the resulting string: