`Predef.Seq` is not necessarily immutable
skolberg opened this issue · comments
Disclaimer: This has already been described here. But after visiting your scala days talk and reading the companion page, I found this kinda missing.
Say I want to write a sum function (just as an example)
def sum(nums: Seq[Int]): Int = nums.reduce(_ + _)
One could write the following code.
val nums = scala.collection.mutable.ArrayBuffer(1, 2, 3)
sum(nums)
This maybe OK in general. However, I am not sure if it should be OK.
The following code is total bogus but it illustrates that misuse is easily accomplished.
val nums = scala.collection.mutable.ArrayBuffer(1, 2, 3)
Future { sum(nums) } onComplete { println }
nums += 4
So, what's the output?
Wouldn't it be better to always explicitly require an immutable.Seq?
Agree. Although this change in 2.13, where the default imported Seq is scala.collection.immutable.Seq[A] instead of scala.collection.Seq[A]. Should markdown have metadata about the version it applies to?
Nice, I didn't know that,
Scala version in markdown metadata would (imho) only be useful if it is rendered, too. I don't know what is possible there, but a 'code comment' on top of the snippet would probably be sufficient, too.
/* ScalaVersion <= 2.12 */
...
The fact that this problem is fixed in 2.13 is not (yet) terribly relevant - a fair amount of the things I talk about are fixed or improved in 2.13, 2.14 or Dotty.
I mean, it is important, but it's a wider issue with the site - I need to somehow flag which version of Scala a rule is relevant for, not just this specific one.
I think I will add this wart, you're right. It's a trap that can definitely catch people off guard.