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Pattern matching is a way of checking the given sequence of tokens for the presence of the specific pattern. It is the most widely used feature in Scala. It is a technique for checking a value against a pattern. It is similar to the switch statement of Java and C.
Notes. Scala's pattern matching statement is most useful for matching on algebraic types expressed via case classes. Scala also allows the definition of patterns independently of case classes, using unapply methods in extractor objects.
It is defined in Scala's root class Any and therefore is available for all objects. The match method takes a number of cases as an argument. Each alternative takes a pattern and one or more expressions that will be performed if the pattern matches. A symbol => is used to separate the pattern from the expressions.
When pattern matching, we assert that a certain piece of data is equal to a certain pattern. For example, in the function: head (element:list) = element. We assert that the first element of head 's argument is called element, and the function returns this.
What you're looking for is a stable identifier. In Scala, these must either start with an uppercase letter, or be surrounded by backticks.
Both of these would be solutions to your problem:
def mMatch(s: String) = {
val target: String = "a"
s match {
case `target` => println("It was" + target)
case _ => println("It was something else")
}
}
def mMatch2(s: String) = {
val Target: String = "a"
s match {
case Target => println("It was" + Target)
case _ => println("It was something else")
}
}
To avoid accidentally referring to variables that already existed in the enclosing scope, I think it makes sense that the default behaviour is for lowercase patterns to be variables and not stable identifiers. Only when you see something beginning with upper case, or in back ticks, do you need to be aware that it comes from the surrounding scope.
You can also assign it to a temporary variable inside the case and then compare it, that will also work
def mMatch(s: String) = {
val target: String = "a"
s match {
case value if (value ==target) => println("It was" + target) //else {} optional
case _ => println("It was something else")
}
}
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