Why does this Scala placeholder not work -

this question has answer here:

given these case classes:

case class featuredistance(id: long, distance: double)  case class searchresult(score: float, id: long)

why not compile?

val distances = list[featuredistance](featuredistance(1l, 10f))  val results = distances.map(searchresult(0f, _.id))

but does:

val results = distances.map(fd => searchresult(0f, fd.id))

the compilation error says: missing parameter type expanded function ((x$3) => x$3.id)

is because _ scoped map function it's not visible in searchresult.apply call?

after doing bit of research, found post on old scala forums contains quote:

when use "_" place holder anonymous parameter of function, scope of function innermost parenthesis containing it.

so, it's question of scope. suspect has problems otherwise result having nested function calls use more 1 underscore. instance:

//suppose have x:list[list[int]] x.map(_.map(_ + 1))

Current CAD