scala - 'case' keyword appearing without its corresponding 'match' keyword -

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• using 'case' in pairrddfunctions.reducebykey() 1 answer

i going through 1 scala example in 1 of popular spark books. looks strange me, @ least newbie. know how standard match/case construct in scala looks in scala. in example see 'case' being used without corresponding 'match' keyword. valid? or more of typo in book?

val joined = userdata.join(events)// rdd of (userid, (userinfo, linkinfo)) pairs val offtopicvisits = joined.filter { case (userid, (userinfo, linkinfo)) => !userinfo.topics.contains(linkinfo.topic) }.count() 

so if it's not regular match/case, 'case' being used in other context?

thanks

that's called pattern matching anonymous functions in scala specification prior match can dropped same behaviour.

{ case p1 => b1 … case pn => bn } 

is equivalent to:

(x1:s1,…,xk:sk) => (x1,…,xk) match {   case p1 => b1 … case pn => bn } 

which in turn equivalent to:

new scala.functionk[s1,…,sk, t] {   def apply(x1:s1,…,xk:sk): t = (x1,…,xk) match {     case p1 => b1 … case pn => bn   } } 

unless expected type partial function:

new scala.partialfunction[s, t] {   def apply(x: s): t = x match {     case p1 => b1 … case pn => bn   }   def isdefinedat(x: s): boolean = {     case p1 => true … case pn => true     case _ => false   } }