should compile - existential combined with f bounded polymorphism

[jhegedus42]

does not compile :

  trait B[T <: B[T]]
  case class A[T <: B[T]](t: T)

  class C() extends B[C]
  val c: C = new C()

  val r2: A[_]         = A(c)     //compiles
  val r3: A[_]         = A(c)     //compiles fine
  val r4: A[_]         = r3       //compiles fine
  val r5: (A[_])       = (r3)     //compiles fine
  val r6: (A[_], A[_]) = (r3, r3) // does not compile, strange

another snippet:

  import scala.language.existentials


  trait B[T <: B[T]]
  case class A[T <: B[T]](t: T)

  class C() extends B[C]
  val c: C = new C()
  type SomeB = T forSome { type T <: B[T] }
  val r3: A[_<:SomeB]         = A(c)     //compiles fine
  val r4: A[C]         = A(c)     //compiles fine
  val r5: (A[_<:SomeB])       = (r3)     //compiles fine
  val r6:((_<:SomeB),((_<:SomeB))) = (c,c)  // compiles fine
  val r7:(A[_<:SomeB],((_<:SomeB))) = (A(c),c)  // compiles fine
  val r8:(A[_<:SomeB],(A[_<:SomeB])) = (A(c),A(c))  // compiles fine
  val r10:(A[_<:SomeB],(A[_<:SomeB])) = (A(c),r3)  // does NOT compile  - SHOULD COMPILE ?
  val r9:((A[T],A[T]) forSome  {type T<:B[T]}) = ((r4:A[C]),r4)  // does compile
  val r11:((A[T],A[T]) forSome  {type T<:B[T]}) = (r4,r4)  // does  compile

[jhegedus42]

http://stackoverflow.com/questions/43807369/strange-compilation-error-with-scala-existentials-with-f-bounded-polymorphism?noredirect=1#comment74657275_43807369

[SethTisue]

have you done a search for previous tickets in this area (combining type bounds and existentials)? it seems likely this is a duplicate.

the pattern matcher has special handling of existentials, so it's not unheard of for it to matter (as in your example) whether pattern matching is involved or not

as noted on Stack Overflow, you must write Tuple1(...) to get a 1-tuple and make pattern matching happen, just parens isn't enough