How can we trace expressions / print statements with line numbers in Scala? - scala

Question

If you want print statements with line numbers, how do you do it?

Answer 1

Check out Haoyi Li's sourcecode library, I think it gives you what you are looking for.
sourcecode is a small Scala library for that provides common "source
code" context to your program at runtime, similar to Python's
__name__, C++'s __LINE__ or Ruby's __FILE__. For example, you can
ask for the file-name and line number of the current file, either
through the () syntax or via an implicit.
See for example https://github.com/lihaoyi/sourcecode#logging
You can use sourcecode.File and sourcecode.Line to define log
functions that automatically capture their line number and file-name
def log(foo: String)(implicit line: sourcecode.Line, file: sourcecode.File) = {
println(s"${file.value}:${line.value} $foo")
}
log("Foooooo") // sourcecode/shared/src/test/scala/sourcecode/Tests.scala:86 Fooooo

Answer 2

It depends on what you want to do.
With the scala-trace-debug library, you can type something like this:
Debug.trace(1 + 2)
And get this:
"3" in thread main:
path.to.file(file.Scala: 22) // click-able stack trace
You can customize the number of lines of stack trace, like so:
Debug.trace(1 + 2, 3) // 3 lines of stack trace
And if you do info.collaboration_station.debug._, you can even do this:
val three = 3.trace
...
"3" in thread main:
path.to.file(file.Scala: 22)
Finally, there is support for expressions:
Debug.traceExpression{
val myVal = 4
1 + 2 + myVal
}
...
"{
val myVal = 4;
(3).+(myVal)
} -> 7" in thread main:
at main.Main$.main(Main.scala:12)
Unlike the other library, this is more geared toward debugging. If I wanted to provide a history of what was going on and I did not want the user to see a stack trace, I would not use this tool.