scala - trying to print overridden toString method - scala

Question

the bellow code :
scala> class A {
| def hi = "Hello from A"
| override def toString = getClass.getName
| }
defined class A
scala> val a = new A()
a: A = A
scala> a.toString
res10: String = A
scala> println(s"${a.toString}")
$line31.$read$$iw$$iw$A
It is printing ok when using a.toString expression, not when using println(s"${a.toString}"). The problem is getClass.getName. In other cases it works nice.
Thanks in advance for any help

Answer 1

REPL filters its output to hide template wrappings.
$ scala
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_92).
Type in expressions for evaluation. Or try :help.
scala> class A
defined class A
scala> val a = new A
a: A = A#4926097b
scala> a.getClass
res0: Class[_ <: A] = class A
scala> $intp.isettings.
allSettings deprecation deprecation_= maxAutoprintCompletion maxPrintString toString unwrapStrings
scala> $intp.isettings.unwrapStrings = false
$intp.isettings.unwrapStrings: Boolean = false
scala> a.getClass
res1: Class[_ <: A] = class $line3.$read$$iw$$iw$A
You can also compare output clipping:
scala> (1 to 1000).mkString
res2: String = 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788899091929394959697989910010110210310410510610710810911011111211311411511611711811912012112212312412512612712812913013113213313413513613713813914014114214314414514614714814915015115215315415515615715815916016116216316416516616716816917017117217317417517617717817918018118218318418518618718818919019119219319419519619719819920020120220320420520620720820921021121221321421521621721821922022122222322422522622722822923023123223323423523623723823924024124224324424524624724824925025125225325425525625725825926026126226326426526626726826927027127227327427527627727827928028128228328428528628728828929029129229329429529629...
scala> println((1 to 1000).mkString)
1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991001011021031041051061071081091101111121131141151161171181191201211221231241251261271281291301311321331341351361371381391401411421431441451461471481491501511521531541551561571581591601611621631641651661671681691701711721731741751761771781791801811821831841851861871881891901911921931941951961971981992002012022032042052062072082092102112122132142152162172182192202212222232242252262272282292302312322332342352362372382392402412422432442452462472482492502512522532542552562572582592602612622632642652662672682692702712722732742752762772782792802812822832842852862872882892902912922932942952962972982993003013023033043053063073083093103113123133143153163173183193203213223233243253263273283293303313323333343353363373383393403413423433443453463473483493503513523533543553563573583593603613623633643653663673683693703713723733743753763773783793803813823833843853863873883893903913923933943953963973983994004014024034044054064074084094104114124134144154164174184194204214224234244254264274284294304314324334344354364374384394404414424434444454464474484494504514524534544554564574584594604614624634644654664674684694704714724734744754764774784794804814824834844854864874884894904914924934944954964974984995005015025035045055065075085095105115125135145155165175185195205215225235245255265275285295305315325335345355365375385395405415425435445455465475485495505515525535545555565575585595605615625635645655665675685695705715725735745755765775785795805815825835845855865875885895905915925935945955965975985996006016026036046056066076086096106116126136146156166176186196206216226236246256266276286296306316326336346356366376386396406416426436446456466476486496506516526536546556566576586596606616626636646656666676686696706716726736746756766776786796806816826836846856866876886896906916926936946956966976986997007017027037047057067077087097107117127137147157167177187197207217227237247257267277287297307317327337347357367377387397407417427437447457467477487497507517527537547557567577587597607617627637647657667677687697707717727737747757767777787797807817827837847857867877887897907917927937947957967977987998008018028038048058068078088098108118128138148158168178188198208218228238248258268278288298308318328338348358368378388398408418428438448458468478488498508518528538548558568578588598608618628638648658668678688698708718728738748758768778788798808818828838848858868878888898908918928938948958968978988999009019029039049059069079089099109119129139149159169179189199209219229239249259269279289299309319329339349359369379389399409419429439449459469479489499509519529539549559569579589599609619629639649659669679689699709719729739749759769779789799809819829839849859869879889899909919929939949959969979989991000
Scroll right to see the ellipsis on the first line.

Answer 2

Since names of classes inside REPL are different, REPL needs to convert internal names back. It does it well enough when displaying strings, but fails when string is passed to an external method, e.g. println or toList:
scala> a.toString
res1: String = A
scala> a.toString.toList
res2: List[Char] = List($, l, i, n, e, 4, ., $, r, e, a, d, $, $, i, w, $, $, i, w, $, A)
scala> "$line4.$read$$iw$$iw$A"
res3: String = A

Answer 3

Run the scala repl using: scala -Xprint:parser
Then run the successive commands. The output $line3.$read$$iw$$iw$A represents the path to the A object. $line is a package, $read and $iw are objects under which the object A is nested.
For the case of println(s"${a.toString}")
scala> println(s"${a.toString}")
[[syntax trees at end of parser]] // <console>
package $line5 {
object $read extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
object $iw extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
import $line3.$read.$iw.$iw.A;
import $line4.$read.$iw.$iw.a;
object $iw extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
val res0 = println(StringContext("", "").s(a.toString))
}
}
}
}
[[syntax trees at end of parser]] // <console>
package $line5 {
object $eval extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
lazy val $result = $line5.$read.$iw.$iw.res0;
lazy val $print: String = {
$line5.$read.$iw.$iw;
"" <-- // SOMETHING OFF HERE! NO OUTPUT STRING BEING GENERATED?
}
}
}
$line3.$read$$iw$$iw$A
Now for the case of a.toString:
scala> a.toString
[[syntax trees at end of parser]] // <console>
package $line6 {
object $read extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
object $iw extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
import $line3.$read.$iw.$iw.A;
import $line4.$read.$iw.$iw.a;
object $iw extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
val res1 = a.toString
}
}
}
}
[[syntax trees at end of parser]] // <console>
package $line6 {
object $eval extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
lazy val $result = $line6.$read.$iw.$iw.res1;
lazy val $print: String = {
$line6.$read.$iw.$iw; // *CORRECTLY GENERATES THE RESULT STRING.*
"".$plus("res1: String = ").$plus(scala.runtime.ScalaRunTime.replStringOf($line6.$read.$iw.$iw.res1, 1000))
}
}
}
res1: String = A

Answer 4

It is the way REPL is compiling A. In a simple app like below there are no issues
Each line in the REPL is wrapped into it's own package.. and that auto generated package name is what you see prepended to class name A.
object ScalaApp extends App {
class A {
def hi = "Hello from A"
override def toString = getClass.getName
}
val a = new A()
println(a.toString)
println(s"${a.toString}")
}