compiler doesn't allow to define matching .apply manually

[HuStmpHrrr]

following code generates error, which is not expected:

Welcome to Scala 2.12.1 (OpenJDK 64-Bit Server VM, Java 1.8.0_131).
Type in expressions for evaluation. Or try :help.

scala> :paste
// Entering paste mode (ctrl-D to finish)

case class Foo(s: String)
object Foo { def apply(s: String) = new Foo(s) }

// Exiting paste mode, now interpreting.

<pastie>:13: error: method apply is defined twice;
  the conflicting method apply was defined at line 14:25
       case class Foo(s: String)

from the specification:

If the object c already has a matching apply (or unapply) member, no new definition is added.

obviously, I am defining a matching .apply, hence the compiler shouldn't complain and simply accept my definition, instead of adding another definition of .apply. this behavior doesn't comply to the specification.

[SethTisue]

You're on 2.12.1, but this wasn't allowed until 2.12.2.

[HuStmpHrrr]

@SethTisue can you elaborate? this part has existed at least in 2.11:

https://www.scala-lang.org/files/archive/spec/2.11/05-classes-and-objects.html#case-classes

[SethTisue]

it was added in 2.11.11; see https://github.com/scala/scala/releases/tag/v2.11.11. 2.12.2 includes all the 2.11.9/2.11.10/2.11.11 changes; see https://github.com/scala/scala/releases/tag/v2.12.2

in 2.12.2, you can do it by default, but in 2.11.11, a late decision was made to put it behind -Xsource:2.12 instead of having it enabled by default. at that time that decision was made, the 2.11 spec change should also have been reverted. a PR fixing that in the 2.11 spec would be welcome

[SethTisue]

note that in general, it isn't valid to reason that everything you see in any 2.11.x release is also present in every 2.12.x release. some 2.11.x releases are newer than some 2.12.x releases