Peculiar types for Paths that differ between Scala 2 and 3

[SethTisue]

starting at os.root, what types result as we add path segments one at a time?

in Scala 2.13.10, we start at Path, take a brief detour to os.root.ThisType, and then we're back at Path

scala> os.root
val res4: os.Path = /

scala> os.root / "a"
val res5: os.root.ThisType = /a

scala> os.root / "a" / "b"
val res6: os.Path = /a/b

scala> os.root / "a" / "b" / "c"
val res7: os.Path = /a/b/c

on Scala 3, the types just keep getting longer:

scala> os.root
val res0: os.Path = /
                                                                                                    
scala> os.root / "a"
val res1: os.root.ThisType = /a
                                                                                                    
scala> os.root / "a" / "b"
val res2: os.root.ThisType#ThisType = /a/b
                                                                                                    
scala> os.root / "a" / "b" / "c"
val res3: os.root.ThisType#ThisType#ThisType = /a/b/c

not sure whether we could do better here, either with changes to the library, or with changes to the compiler, or both

[lefou]

I think Scala 3 is more correct here, as we use a type ThisType <: BasePath as return value. Maybe the use of this.type helps here.

[lefou]

No, I think this.type can't work, as we want to return new instances of immutable classes.

[lefou]

• I opened PR Be more specific in return type of make and /. #154

[SethTisue]

Nice! Glad it turned out to be tractable to do something about this.

[SethTisue]

incidentally the context where this came up for me was scalacenter/docs.scala-lang#21