Why does one of these statements compile in Scala but not the other?
- by Jeff
(Note: I'm using Scala 2.7.7 here, not 2.8).
I'm doing something pretty simple -- creating a map based on the values in a simple, 2-column CSV file -- and I've completed it easily enough, but I'm perplexed at why my first attempt didn't compile. Here's the code:
// Returns Iterator[String]
private def getLines = Source.fromFile(csvFilePath).getLines
// This doesn't compile:
def mapping: Map[String,String] = {
Map(getLines map { line: String =>
val pairArr = line.split(",")
pairArr(0) -> pairArr(1).trim()
}.toList:_*)
}
// This DOES compile
def mapping: Map[String,String] = {
def strPair(line: String): (String,String) = {
val pairArr = line.split(",")
pairArr(0) -> pairArr(1).trim()
}
Map(getLines.map( strPair(_) ).toList:_*)
}
The compiler error is
CsvReader.scala:16:
error: value toList is not a member of
(St ring) = (java.lang.String,
java.lang.String) [scalac] possible
cause: maybe a semicolon is missing
before `value toList'? [scalac]
}.toList:_*) [scalac] ^
[scalac] one error found
So what gives? They seem like they should be equivalent to me, apart from the explicit function definition (vs. anonymous in the nonworking example) and () vs. {}. If I replace the curly braces with parentheses in the nonworking example, the error is "';' expected, but 'val' found." But if I remove the local variable definition and split the string twice AND use parens instead of curly braces, it compiles. Can someone explain this difference to me, preferably with a link to Scala docs explaining the difference between parens and curly braces when used to surround method arguments?
