Q: "non-literal range" explanation?

[jpsacha]

For a line of code:

cfor(myRange) { i =>

I am getting "[Info]" printed during compilation, with message "non-literal range". I assume that it is generated by cfor.
How to interpret that message? Does it have performance implications?

Note, myRange is passed as an argument to the function that is using cfor.

[shuttie]

I guess the reason is that non-literal ranges (so ranges, defined outside of the cfor context) cannot be effectively rewritten in a simple while loop. So two examples:

// range is within macro context
cfor(0 until 100 step 5) { i => ???}
// so we expand it into this loop
var i = 0
while (i < 100) {
   ???
   i += 5
}

// here the range itself is outside of the cfor macro context, so it cannot know the shape of the range
val range = 0 until 100 step 5
cfor(range) { i => ???}
// so we expand it into a foreach over range, which is also a nice and fast method to use
range.foreach { i => ???}

I guess I need to clarify this warning a bit:

• add benchmarks on literal and non-literal ranges (I bet they will be almost the same)
• maybe expand non-literal ranges into another shape of while loop?
• more clear warning message in this macro (if my attempt on non-literal expansion fails)

[jpsacha]

thanks for the explanation