stack overflow - scala implicit causes StackOverflowError -

how implicit val cause stackoverflowerror?

(pared down original code, still cause error)

object complicit {   // class name, default, , conversion function implicit val   case class cc[a](name: string, defaultvalue: a)(implicit val convert: string => a) {     def getfrom(s: string): a= try {        convert(s)      } catch {        case t: throwable =>          println("error: %s".format(t))  // see stackoverflowexception         defaultvalue     }   }      // works fine   object works {     val cc1= cc("first", 0.1)(_.todouble)   }     // causes java.lang.stackoverflowerror due implicit   object fails {     // !!! stackoverflowerror here     implicit val stringtodouble: string => double= { _.todouble }      val cc2= cc("second", 0.2)   }    def main(args: array[string]) {     // works     println("%s %f".format(works.cc1.name, works.cc1.getfrom("2.3")))     // fails     println("%s %f".format(fails.cc2.name, fails.cc2.getfrom("4.5")))   } }   

am doing illegal implicits?

i believe can answer what's happening here.. it's related other implicit conversions, , 1 created. if add trace can confirm stack overflow relates - function calling repeatedly until stack space of java crashes:

implicit val stringstodouble: string => double= { x=>println("called inner "+x); x.todouble } 

.... called inner 4.5 called inner 4.5 called inner 4.5 called inner 4.5 called inner 4.5error: java.lang.stackoverflowerror

i think what's happening - todouble not natural function of java string, rather happens using implicit conversion in stringops (or stringlike, i'm not sure it's same issue).

so when call todouble - compiler starts seeking implicit conversion contain function "todouble". in theory resulting class.

but - should happen if several implicit conversions achieve this? unfortunately, "double" contains function todouble proven here:

val x = 44.4 x.todouble 

and guess what? means new implicit function, closest in scope wins contest , get's called in circle accomplish "todouble" - trying turn string double, in order call todouble (on class double), repeatedly.. i'll admit it's confusing, evidence fits.

here's fix.. fits explanation , prevents recursive calls.

 implicit val stringstodouble: string => double= { java.lang.double.parsedouble(_)  }