type mismatch errors when upgrading from scala 2.9 to 2.13.2

Blankman_39677 0
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I recently revived an old library that was written in scala 2.9, and I created a new scala project using scala 2.13.2

I am getting errors like the following:

type mismatch;
found   : scala.collection.mutable.Buffer[Any]
[error]  required: Seq[Any]

Was there a specific change between 2.9 to 2.13.2 that involved not implicitly casting sequences or something that might solve many of these types of compile errors?

I had to add .toSeq to many of my function return statements that were vals of Buffer[Any] that needed to be passed as an arguement to a function expected a Sequence.

scala
2 Answers

Quite a lot things happened in the last 7+ years (including rewrite of the collections library).

If adding .toSeq solves your problem - just go for it.

If you want to know what exactly has changed - try upgrading version-by version: first upgrade to scala-2.10., then to 2.11., then 2.12.*, then, finally, to 2.13.2.

At each upgrade you'll probably see deprecation warnings. Fix them before upgrading to the next version.

user_53850410

Brave, but perhaps bad form, to disturb the dead. Nevertheless, maybe pass mutable.Buffer as mutable.Seq instead of Seq which is by default immutable.Seq. Consider

val mb = mutable.Buffer(11, Some(42))
val ms: mutable.Seq[Any] = mb // OK
val is: Seq[Any] = mb         // NOK
user_52050220
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