generics - Scala nested case class self-bounding inheritance -


i'm working on a* implementation in scala. accomplish clean structure use nested case class structure implements self-bounded trait. however, experience issues when implementing in scala ide. following code not compile:

trait a[t <: a[t]]  class b {      case class c(int: int) extends a[c] // a[this.c] won't work either      def make = c(5)  }  object d {      def foo[t <: a[t]](some: t) = {}      val c = new b().make      foo(c) // not compile  }

is there way can make structure work?

not sure why want this, here's why won't work is:

the type of d.c b#c. path-dependent type don't know instance of b belongs to. however, c extends a[c], same saying a[this.c] in context, bound specific instance of b. foo sees type parameter t b#c, not same b.c b.

you have 2 options make compile.

relax constraints of a b#c:

trait a[t <: a[t]]  class b {      case class c(int: int) extends a[b#c]      def make = c(5)  }  object d {      def foo[t <: a[t]](some: a[t]) = {}      val c = new b().make      foo(c)  }

or handle path-dependent type, c has type b.c:

trait a[t <: a[t]]  class b {      case class c(int: int) extends a[c]      def make = c(5)  }  object d {      def foo[t <: a[t]](some: a[t]) = {}      val b = new b     val c: b.c = b.make      foo(c)  }

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