Diagnosing Scala compile error “value to is not a member of Int”

Question

I made a code change within a Scala class that had been working fine. Upon trying to compile the modification, the compiler spit out the error message, "value to is not a member of Int" relating to this (pre-existing) line of code:

for (i <- 0 to cColumn -1) { ... }

Doing some research, I came across some bug reports on the "to" method - and also that "to" is apparently a method provided within the intWrapper class(?).

So, based upon that info, I started looking at my class's import statements... no such import for intWrapper. (Q: That being the case, how did this ever compile/run in the first place?) What makes this even more interesting (to me) is that when I started to do a global search in the codebase for that import I accidentally terminated the compiler (sbt) session...but when I restarted it, the class compiled just fine. No errors at all. (And no code changes from the previous session)

Anyone have any ideas as to what would cause this intermittent behavior?

NOTES:
1) using Scala 2.10.2 with javac 1.7.0_25
2) the code change to the class had nothing to do with the example functionality, nor did it alter any of the class's imports

Update: Here are the variable declarations:

val meta = rs.getMetaData()
val cColumn = meta.getColumnCount()

EDIT: Per suggestion, here is the test lines (all of them compile fine now):

implicitly[scala.Int => scala.runtime.RichInt]
intWrapper(3) to 4
for (i <- 0 to 33 -1) { /* do something smart */ }

for (i <- 0 to cColumn -1) { ... }

EDIT 2 Here is the full compiler error:

[error] /path/to/src/file/DBO.scala:329: value to is not a member of Int
[error]       for (i <- 0 to cColumn -1) {
[error]

That error was repeating ~18 times in the class. (It's a DBO-DB interface layer); where DBO.scala is the file containing the newly modified trait.

Answer 1

I just encountered this same issue. In my case, it was caused by an unnecessary import, like this:

import scala.Predef.String

class Test() {
  for (t <- 1 to 3) {}
}  

By default, Scala imports all of scala.Predef. Predef extends LowPriorityImplicits, which includes an implicit conversion from Int to RichInt.

to is actually defined on RichInt, so you need this conversion in order to use it. By importing just part of Predef, I lose this conversion. Get rid of the unnecessary import and the error goes away.

Answer 2

how did this ever compile/run in the first place?

By default, the contents of scala.Predef is imported. There you have method intWrapper which produces a RichInt with method to.

You probably have shadowed symbol intWrapper. Does the following work:

implicitly[scala.Int => scala.runtime.RichInt]

or this:

intWrapper(3) to 4

...if not, there lies your problem.

---

EDIT: So, since you say that compiles, what happens is you replace cColumn with a constant, e.g.

for (i <- 0 to 33 -1) { ... }

? It would also help to post the complete compiler message with indicated line etc.

Answer 3

Without knowing where that error comes from, you might also try to work around it by constructing the Range by hand:

for (i <- Range.inclusive(0, cColumn-1)) { ... }

or

Range.inclusive(0, cColumn-1).foreach { i => ... }