I'm starting to learn Lift and I'm stuck. I have problem with simple snippet:
class Util {
def in(html: NodeSeq) : NodeSeq ={
if (User.loggedIn_?)
Helpers.bind("user", html, "name" -> User.currentUser.map(_.lastName).open_!)
else
NodeSeq.Empty
}
It should inject current User name, but I'm receiving exception:
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.scala_tools.maven.executions.MainHelper.runMain(MainHelper.java:105)
at org.scala_tools.maven.executions.MainWithArgsInFile.main(MainWithArgsInFile.java:26)
Caused by: scala.tools.nsc.symtab.Types$TypeError: type mismatch;
found : x$1.lastName.type (with underlying type object x$1.lastName)
required: com.liftworkshop.model.User#lastName.type
at scala.tools.nsc.typechecker.Contexts$Context.error(Contexts.scala:352)
What is going on?
The problem here is that _.lastName is actually a singleton object of type MappedString and not the actual string value. To get at the String value you should do:
_.lastName.is
Related
I've this small scala code snipet:
#SerialVersionUID(43L) class p(val a:Int=14,val b:Double=3.0) extends Serializable{
}
import java.io._
val out = new ObjectOutputStream(new FileOutputStream("my.obj"))
out.writeObject(new p(5,7))
out.close()
val in = new ObjectInputStream(new FileInputStream("my.obj"))
val savedPerson=in.readObject.asInstanceOf[p]
println(savedPerson.a)
When I run it on windows or mac, it prints out a huge exception information:
java.io.NotSerializableException: Main$$anon$1
at java.base/java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.base/java.io.ObjectOutputStream.defaultWriteFields(Unknown Source)
at java.base/java.io.ObjectOutputStream.writeSerialData(Unknown Source)
at java.base/java.io.ObjectOutputStream.writeOrdinaryObject(Unknown Source)
at java.base/java.io.ObjectOutputStream.writeObject0(Unknown Source)
at java.base/java.io.ObjectOutputStream.writeObject(Unknown Source)
at Main$$anon$1.errorFunction(ch09.scala:52)
at Main$$anon$1.<init>(ch09.scala:110)
at Main$.main(ch09.scala:1)
at Main.main(ch09.scala)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.base/java.lang.reflect.Method.invoke(Unknown Source)
at scala.reflect.internal.util.ScalaClassLoader.$anonfun$run$2(ScalaClassLoader.scala:98)
at scala.reflect.internal.util.ScalaClassLoader.asContext(ScalaClassLoader.scala:32)
at scala.reflect.internal.util.ScalaClassLoader.asContext$(ScalaClassLoader.scala:30)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:129)
at scala.reflect.internal.util.ScalaClassLoader.run(ScalaClassLoader.scala:98)
at scala.reflect.internal.util.ScalaClassLoader.run$(ScalaClassLoader.scala:90)
at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:129)
at scala.tools.nsc.CommonRunner.run(ObjectRunner.scala:22)
at scala.tools.nsc.CommonRunner.run$(ObjectRunner.scala:21)
at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
at scala.tools.nsc.CommonRunner.runAndCatch(ObjectRunner.scala:29)
at scala.tools.nsc.CommonRunner.runAndCatch$(ObjectRunner.scala:28)
at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
at scala.tools.nsc.ScriptRunner.runCompiled(ScriptRunner.scala:170)
at scala.tools.nsc.ScriptRunner.$anonfun$runScript$1(ScriptRunner.scala:187)
at scala.tools.nsc.ScriptRunner.$anonfun$runScript$1$adapted(ScriptRunner.scala:187)
at scala.tools.nsc.ScriptRunner.$anonfun$withCompiledScript$2(ScriptRunner.scala:156)
at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:124)
at scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala:200)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:70)
at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:85)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:101)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
What error is this? How can I fix it? I don't quite get this.
Thanks!
I see from your stack trace that you're using the script runner:
scala -nc noser.scala
where I've named the script as in Yessir, no sir, because there is no serialization happening.
-nc avoids starting the compile server daemon.
If the script runner doesn't see an object with a main method, it packages your script code in a class that is local to a main method it constructs for you.
def main(args: Array[String]) = { class anon_class { code } ; new anon_class() }
Your code is run in the constructor, which isn't a good idea either.
You can see this with -Xprint:typer,flatten. Or experiment with -Xprint:all.
Your serializable class has an outer pointer to the anonymous local class, and the anonymous class is not serializable.
Maybe the outer pointer is just a bug. Or not, see the reference below. It needs a hint to eliminate the outer pointer, such as making the class final.
I see there have been similar bugs such as this one where the enclosing module is captured by a lambda.
Your workaround is to put your code in the main method of an object, or wrap everything in App.
object Main extends App {
// code
}
Another workaround is to make your serializable class final. There is discussion on this ticket and the related ticket and fix.
I'm, working on refactoring our code so that we can use the CAKE pattern for DI.
I've stumbled upon a serialisation issue which I'm having difficulty in understanding.
When I call this function:
def getAccounts(winZones: Broadcast[List[WindowsZones]]): RDD[AccountDetails] = {
val accounts = getAccounts //call to db
val result = accounts.map(row =>
Some(AccountDetails(UUID.fromString(row.getAs[String]("")),
row.getAs[String](""),
UUID.fromString(row.getAs[String]("")),
row.getAs[String](""),
row.getAs[String](""),
DateUtils.getIanaZoneFromWinZone(row.getAs[String]("timeZone"), winZones))))
.map(m=>m.get)
result
}
it works perfectly, but this is ugly and I want to refactor it so that the middle mapping from row to AccountDetails is placed inside a private function - but when doing that it causes the serialisation issue.
I'd like:
def getAccounts(winZones: Broadcast[List[WindowsZones]]): RDD[AccountDetails] = {
val accounts = getAccounts
val result = accounts
.map(m => getAccountDetails(m, winZones))
.filter(_.isDefined)
.map(m => m.get)
result
}
private def getAccountDetails(row: Row, winZones: Broadcast[List[WindowsZones]]): Option[AccountDetails] = {
try {
Some(AccountDetails(UUID.fromString(""),
row.getAs[String](""),
UUID.fromString(row.getAs[String]("")),
row.getAs[String](""),
row.getAs[String](""),
DateUtils.getIanaZoneFromWinZone(row.getAs[String]("timeZone"), winZones)))
}
catch {
case e: Exception =>
logger.error(s"Unable to set AccountDetails $e")
None
}
}
Any help is appreciated of course, the AccountDetails obj is a case class should that be pertinent. Also happy to take any other advice on implementing cake or DI with spark in general. Thanks.
Edit to show structure:
trait serviceImpl extends anotherComponent {this: DBA =>
def Accounts = new Accounts
class Accounts extends AccountService {
//the methods above are defined here.
}
Edit to include stacktrace:
17/02/13 17:32:32 INFO CodeGenerator: Code generated in 271.36617 ms
Exception in thread "main" org.apache.spark.SparkException: Task not serializable
at org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:298)
at org.apache.spark.util.ClosureCleaner$.org$apache$spark$util$ClosureCleaner$$clean(ClosureCleaner.scala:288)
at org.apache.spark.util.ClosureCleaner$.clean(ClosureCleaner.scala:108)
at org.apache.spark.SparkContext.clean(SparkContext.scala:2039)
at org.apache.spark.rdd.RDD$$anonfun$map$1.apply(RDD.scala:366)
at org.apache.spark.rdd.RDD$$anonfun$map$1.apply(RDD.scala:365)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151)
at org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:112)
at org.apache.spark.rdd.RDD.withScope(RDD.scala:358)
at org.apache.spark.rdd.RDD.map(RDD.scala:365)
at FunnelServiceComponentImpl$FunnelAccounts.getAccounts(FunnelServiceComponentImpl.scala:24)
at Main$.delayedEndpoint$Main$1(Main.scala:26)
at Main$delayedInit$body.apply(Main.scala:7)
at scala.Function0$class.apply$mcV$sp(Function0.scala:34)
at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
at scala.App$$anonfun$main$1.apply(App.scala:76)
at scala.App$$anonfun$main$1.apply(App.scala:76)
at scala.collection.immutable.List.foreach(List.scala:381)
at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:35)
at scala.App$class.main(App.scala:76)
at Main$.main(Main.scala:7)
at Main.main(Main.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: java.io.NotSerializableException: FunnelServiceComponentImpl$FunnelAccounts
Serialization stack:
- object not serializable (class: FunnelServiceComponentImpl$FunnelAccounts, value: FunnelServiceComponentImpl$FunnelAccounts#16b7e04a)
- field (class: FunnelServiceComponentImpl$FunnelAccounts$$anonfun$1, name: $outer, type: class FunnelServiceComponentImpl$FunnelAccounts)
- object (class FunnelServiceComponentImpl$FunnelAccounts$$anonfun$1, <function1>)
at org.apache.spark.serializer.SerializationDebugger$.improveException(SerializationDebugger.scala:40)
at org.apache.spark.serializer.JavaSerializationStream.writeObject(JavaSerializer.scala:46)
at org.apache.spark.serializer.JavaSerializerInstance.serialize(JavaSerializer.scala:100)
at org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:295)
... 26 more
17/02/13 17:32:32 INFO SparkContext: Invoking stop() from shutdown hook
Where are you defining the functions?
Let's say you are defining them in a class X. If the class is not serializable this would cause your issue.
To solve this you can either make it an object instead or make the class serializable.
Because getAccountDetails is in your class, Spark will want to serialize your entire FunnelAccounts object. After all, you need an instance in order to use this method. However, FunnelAccounts is not serializable. Thus it can't be sent off to a worker.
In your case, you should move getAccountDetails into a FunnelAccounts object, so that you don't need an instance FunnelAccounts to run it.
I was searching for secondary sort using Spark and found this solution:
case class RFMCKey(cId: String, R: Double, F: Double, M: Double, C: Double)
class RFMCPartitioner(partitions: Int) extends Partitioner {
require(partitions >= 0, "Number of partitions ($partitions) cannot be negative.")
override def numPartitions: Int = partitions
override def getPartition(key: Any): Int = {
val k = key.asInstanceOf[RFMCKey]
k.cId.hashCode() % numPartitions
}
}
object RFMCKey {
implicit def orderingBycId[A <: RFMCKey] : Ordering[A] = {
Ordering.by(k => (k.R, k.F * -1, k.M * -1, k.C * -1))
}
}
Now this is the code that I am using for my RFMC (Recency, Frequency, Monetary, Clumpiness) program.
In the same code, at the end, I am doing:
val rfmcTableSorted = rfmcTable.repartitionAndSortWithinPartitions(new RFMCPartitioner(1))
But when I load this file in spark-shell, I get the following error:
<console>:130: error: RFMCKey is already defined as (compiler-generated) case class companion object RFMCKey
object RFMCKey {
^
<console>:198: error: RFMCKey.type does not take parameters
case (custId, (((rVal, fVal), mVal),cVal)) => (RFMCKey(custId, rVal, fVal, mVal, cVal), rVal+","+fVal+","+mVal+","+cVal)
^
<console>:200: error: value repartitionAndSortWithinPartitions is not a member of org.apache.spark.rdd.RDD[Nothing]
val rfmcTableSorted = rfmcTable.repartitionAndSortWithinPartitions(new RFMCPartitioner(1)).cache()
How do I circumvent this issue?
Update 1
I tried changing the order of declaration of my case class and object class and surprisingly the shell loaded the file without throwing any errors. But when I ran my program it threw a new error:
org.apache.spark.SparkException: Task not serializable
at org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:166)
at org.apache.spark.util.ClosureCleaner$.clean(ClosureCleaner.scala:158)
at org.apache.spark.SparkContext.clean(SparkContext.scala:1623)
at org.apache.spark.rdd.RDD.map(RDD.scala:286)
at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$.constructRFMC(<console>:113)
at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:36)
at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:41)
at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:43)
at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:45)
at $iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:47)
at $iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:49)
at $iwC$$iwC$$iwC$$iwC.<init>(<console>:51)
at $iwC$$iwC$$iwC.<init>(<console>:53)
at $iwC$$iwC.<init>(<console>:55)
at $iwC.<init>(<console>:57)
at <init>(<console>:59)
at .<init>(<console>:63)
at .<clinit>(<console>)
at .<init>(<console>:7)
at .<clinit>(<console>)
at $print(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.spark.repl.SparkIMain$ReadEvalPrint.call(SparkIMain.scala:1065)
at org.apache.spark.repl.SparkIMain$Request.loadAndRun(SparkIMain.scala:1338)
at org.apache.spark.repl.SparkIMain.loadAndRunReq$1(SparkIMain.scala:840)
at org.apache.spark.repl.SparkIMain.interpret(SparkIMain.scala:871)
at org.apache.spark.repl.SparkIMain.interpret(SparkIMain.scala:819)
at org.apache.spark.repl.SparkILoop.reallyInterpret$1(SparkILoop.scala:856)
at org.apache.spark.repl.SparkILoop.interpretStartingWith(SparkILoop.scala:901)
at org.apache.spark.repl.SparkILoop.command(SparkILoop.scala:813)
at org.apache.spark.repl.SparkILoop.processLine$1(SparkILoop.scala:656)
at org.apache.spark.repl.SparkILoop.innerLoop$1(SparkILoop.scala:664)
at org.apache.spark.repl.SparkILoop.org$apache$spark$repl$SparkILoop$$loop(SparkILoop.scala:669)
at org.apache.spark.repl.SparkILoop$$anonfun$org$apache$spark$repl$SparkILoop$$process$1.apply$mcZ$sp(SparkILoop.scala:996)
at org.apache.spark.repl.SparkILoop$$anonfun$org$apache$spark$repl$SparkILoop$$process$1.apply(SparkILoop.scala:944)
at org.apache.spark.repl.SparkILoop$$anonfun$org$apache$spark$repl$SparkILoop$$process$1.apply(SparkILoop.scala:944)
at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
at org.apache.spark.repl.SparkILoop.org$apache$spark$repl$SparkILoop$$process(SparkILoop.scala:944)
at org.apache.spark.repl.SparkILoop.process(SparkILoop.scala:1058)
at org.apache.spark.repl.Main$.main(Main.scala:31)
at org.apache.spark.repl.Main.main(Main.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:569)
at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:166)
at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:189)
at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:110)
at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala)
Caused by: java.io.NotSerializableException: $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$
Serialization stack:
- object not serializable (class: $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$, value: $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$#757fc606)
- field (class: $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$$anonfun$17, name: $outer, type: class $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$)
- object (class $iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$rfmc$$anonfun$17, <function1>)
at org.apache.spark.serializer.SerializationDebugger$.improveException(SerializationDebugger.scala:38)
at org.apache.spark.serializer.JavaSerializationStream.writeObject(JavaSerializer.scala:47)
at org.apache.spark.serializer.JavaSerializerInstance.serialize(JavaSerializer.scala:80)
at org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:164)
... 52 more
Update 2
The way I am defining my objects and functions is like this:
object rfmc {
def constructrfmc() = {
// Everything goes inside including the custom key and partitioner
// code defined above
}
}
Update 3
The way I am defining my code in eclipse which works perfectly is:
object rfmc extends App {
// Everything goes inside including the custom key and partitioner
// code defined above
}
I also created a JAR for this code and ran using spark-submit and that too worked perfectly.
To address the issue that RFMCKey is already defined, you need to swap the order of your case class and object declaration as explained in this issue.
Regarding your updates, there may be some limitations in the spark-shell that can't let execute any arbitrary code (such as with accumulators). To get more insight on the serialization mechanism, you should pass the following option -Dsun.io.serialization.extendedDebugInfo=true. Remember that the spark-shell is more of an exploratory utility to test small portions of code or new features iteratively thanks to the REPL, and not a fully-fledged production-ready utility that should be used extensively to test your code.
Your safest option here is to package your app into a jar and set up Spark in standalone mode, and run spark-submit with your packaged jar. As reflected in update 3 and 4 of your post, you'll need to update your code to wrap it into an object so that it is the entry point of your job. This will enable you to make sure your code is not at fault here.
I am trying to define a function that takes an integer and an implicit object that has the code to process that number, but i get a NullPointerException and i don know why.
If I delete the first println the code works.
Is there some problem with the way i am defining the implicit objects?
Here is my code:
class A {
def apply(n : Int) = n*2
}
def f(n: Int)(implicit o : A) = o(n)
implicit val a = new A
println(f(3))
class B extends A {
override def apply(n: Int) = n*3
}
implicit val b = new B
println(f(3))
And this is the error:
java.lang.NullPointerException
at Main$$anon$1.f(open.scala:5)
at Main$$anon$1.<init>(open.scala:8)
at Main$.main(open.scala:1)
at Main.main(open.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at scala.tools.nsc.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:78)
at scala.tools.nsc.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:24)
at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:88)
at scala.tools.nsc.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:78)
at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:33)
at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:40)
at scala.tools.nsc.ScriptRunner.scala$tools$nsc$ScriptRunner$$runCompiled(ScriptRunner.scala:171)
at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:188)
at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:188)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun$apply$mcZ$sp$1.apply(ScriptRunner.scala:157)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun$apply$mcZ$sp$1.apply(ScriptRunner.scala:157)
at scala.Option.exists(Option.scala:187)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply$mcZ$sp(ScriptRunner.scala:157)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:131)
at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:131)
at scala.tools.nsc.util.package$.waitingForThreads(package.scala:26)
at scala.tools.nsc.ScriptRunner.withCompiledScript(ScriptRunner.scala:130)
at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:188)
at scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala:201)
at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:58)
at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:80)
at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
This isn't a problem with implicits per se. The issue is that scala is deciding to use b as the implicit parameter to f for both calls, however b isn't initialized yet when the first call happens. The scala compiler should probably complain about ambiguous implicit values here, but the use of both types A and B seems to confuse it.
I was playing around with Scala's structural types when I discovered what looks like a bug to me. Here is my code:
type toD = { def toDouble: Double }
def foo(t: toD) = t.toDouble
foo(5)
And I got this error:
java.lang.NoSuchMethodException
at scala.runtime.BoxesRunTime.toDouble(Unknown Source)
at .foo(<console>:9)
at .<init>(<console>:11)
at .<clinit>(<console>)
at .<init>(<console>:11)
at .<clinit>(<console>)
at $print(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704)
at scala.tools.nsc.interpreter.IMain$Request$$anonfun$14.apply(IMain.scala:920)
at scala.tools.nsc.interpreter.Line$$anonfun$1.apply$mcV$sp(Line.scala:43)
at scala.tools.nsc.io.package$$anon$2.run(package.scala:25)
at java.lang.Thread.run(Unknown Source)
First, I don't know why this isn't working. Second, it's weird that the code compiles just fine and throws an exception at runtime saying that the method doesn't actually exist.
Does anyone have an explanation for this?
I just played around a bit with this and it really seems to be a bug. However it works when you just set the return type to Any:
type toD = { def toDouble: Any }
I think it may have something to do with auto boxing and the way primitives are handled.
edit:
I just found a workaround:
type toD[A] = { def toDouble: A }
def foo[A](x: toD[A])(implicit y: A =:= Double) = x.toDouble
This ensures, that the return value of toDouble (A) is Double