scala - Pattern match on manifest instances of sealed class -

given classes

sealed abstract class  case class b(param: string) extends  case class c(param: int) extends  trait z {}  class z1 extends z {}  class z2 extends z {}  def zfor[t <: : manifest]: option[z] = {   val z = manifest[t].erasure   if (z == classof[b]) {     some(new z1)   } else   if (z == classof[c]) {     some(new z2)   } else {     none   } } 

i think problem pattern matching here impossibility build pattern matching table in bytecode. there workaround on problem? may can use int generated in manifest compiler?

the way you've written there isn't robust if have more complicated class hierarchy since if have class d <: c, classof[d] != classof[c]. don't want pattern-match anyway. could; can't call classof[x] in middle of pattern-match, can

def zfor[t <: : manifest]: option[z] = {   val classb = classof[b]   val classc = classof[c]   manifest[t].erasure match {     case classb => some(new z1)     case classc => some(new z2)     case _      => none   } } 

as long you're sure you're in situation need detect leaves of class hierarchy. (you should make sure marking b , c final.)

alternatively, can use isassignablefrom perform runtime test:

def zfor2[t <: : manifest]: option[z] = {   manifest[t].erasure match {     case x if classof[b].isassignablefrom(x) => some(new z1)     case x if classof[c].isassignablefrom(x) => some(new z2)     case _                                   => none   } } 

and now

class d extends c(5) {}  scala> zfor[d] res5: option[z] = none  scala> zfor2[d] res6: option[z] = some(z2@2556af33)