Mirror of forum.nim-lang.org

2423 :: type equality with unused generic types

• jxy (orginal) [2016-07-30T04:19:18+02:00] view original

  I'm having trouble upgrading my old code that worked under v0.13. The following snippet no longer works under v0.14.2.

  type
    G[N:static[int]] = object
      v: int
    A = G[1]
    B = G[2]
  static:
    echo(A is B)
  proc p(x:A) = echo "A:",x.v
  proc p(x:B) = echo "B:",x.v
  p(A(v:1))
  p(B(v:2))
  Run

  A and B used to be different types, but under v0.14, A is B. Is it an intended behavior or a regression?

  Edit: It's not related to static types. Any generic type uses unused type parameter no longer creates a distinct type.

---

• jxy (orginal) [2016-07-30T04:41:33+02:00] view original

  With an extra indirection, the following code compiles and runs fine

  type
    G[N:static[int]] = object
      v: int
    A = G[1]
    B = G[2]
  type
    F[U] = object
      v: U
    X = F[A]
    Y = F[B]
  static:
    echo(A is B)
    echo(X is Y)
  proc p(x:X) = echo "X:",x.v.v
  proc p(x:Y) = echo "Y:",x.v.v
  p(X(v:A(v:1)))
  p(Y(v:B(v:2)))
  Run

  This means that A is B while F[A] isnot F[B]. It's inconsistent and confusing. Should F[A] is F[B] if A is B? Or should A isnot B in the first place, since 1 isnot 2.

---