scala - Generic map method for spark RDD doesnt compile -

i can't figure out why doesn't compile:

implicit class debughelper[t](ar: rdd[t]) {     def debug_restrainer(implicit sc: sparkcontext): rdd[t] = {         if (debug_size.isdefined) sc.parallelize(ar.take(debug_size.get)) else ar     } } 

it gives error: no classtag available t

does know it's complaining about?

if compiler asks classtag need. sparkcontext can retrieved existing rdd.

import scala.reflect.classtag  implicit class debughelper[t](ar: rdd[t])(implicit val t: classtag[t]) {   def debug_restrainer: rdd[t] = {     if (debug_size.isdefined)        ar.sparkcontext.parallelize(ar.take(debug_size.get))     else ar   } }