Pattern match for variable in scope (Scala)

In the following c开发者_JAVA技巧ode

val x = 5
val y = 4 match {
  case x => true
  case _ => false
}

the value y is true. Scala interprets x to be a free variable in the pattern match instead of binding it to the variable with the same name in the scope.

How to solve this problem?

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Backticking the variable indicates to bind a scoped variable:

val x = 5
val y = 4 match { case `x` => true; case _ => false }

returns false.

Alternatively, if a variable starts with an uppercase letter, it binds to a scoped variable without backticking.

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Invoking the least astonishment principle, I will simply do:

val x = 5
val y = 4 match {
  case z if z == x => true
  case _ => false
}