gistfile1.txt

type
  A = enum
    b
    c

  K = object
    y*: string
    z*: int

  J = object
    # K and J aren't nominally-related, but structurally-related types
    y*: string
    z*: int

  D* = object
    case e: A
    of b: f*: K
    of c: g*: J

template h(i: D, j: untyped): untyped =
  if i.e == b:
    i.f.j
  else:
    i.g.j

# Deliberately runtime, in principle
let
  m = D(e: b, f: K(y: "foo", z: 3))
  n = D(e: c, g: J(y: "bar", z: 7))

echo h(m, y)
echo h(m, z)

echo h(n, y)
echo h(n, z)