Why can't upper-case letters be used for pattern matching for define values?

Question

Why can I use lower-case letters for names:

val (a, bC) = (1, 2)

(1, 2) match {
  case (a, bC) => ???
}

and can\'t use upper-case lette

Answer 1

Because the designers of Scala preferred to allow identifiers starting with upper-case letters to be used like this (and allowing both would be confusing):

val A = 1

2 match {
  case A => true
  case _ => false
} // returns false, because 2 != A

Note that with lower case you'll get

val a = 1

2 match {
  case a => true
  case _ => false
} // returns true

because case a binds a new variable called a.

One very common case is

val opt: Option[Int] = ...

opt match {
  case None => ... // you really don't want None to be a new variable here
  case Some(a) => ...
}