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  1. object Main {
  2.   trait T { def f: Int }
  3.   case class X(val f: Int) extends T
  4.   case class Y(val f: Int) extends T
  5.  
  6.   /* Can we make the return type more specific with an HList? (I assume not) */
  7.   def create(b: Int => Boolean, x: Int => Option[X], y: Int => Option[Y])
  8.            : List[T] = {
  9.  
  10.     var i = 0
  11.     var ts = List[T]()
  12.  
  13.     while (b(i)) {
  14.       x(i).map{ts ::= _}
  15.       y(i).map{ts ::= _}
  16.  
  17.       i += 1
  18.     }
  19.  
  20.     ts
  21.   }
  22.  
  23.   def main(args: Array[String]) {
  24.     val b = (n: Int) => n < 5
  25.     val x = (n: Int) => if (n % 2 == 0) Some(X(n)) else None
  26.     val y = (n: Int) => if (n % 3 == 0) Some(Y(n)) else None
  27.  
  28.     val ts = create(b, x, y)
  29.     println(ts) /* List(X(4), Y(3), X(2), Y(0), X(0)) */
  30.  
  31.     /* Can we reconstruct static type information at runtime?
  32.      * (I am still not sure what that actually means ...)
  33.      */
  34.   }
  35. }
Success #stdin #stdout 0.27s 247424KB
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List(X(4), Y(3), X(2), Y(0), X(0))
https://ideone.com/sxIw1
language:
Scala (scala 2.12.8)
created:
11 years ago
visibility:
public

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