Calling newColumnView() does not compile.

[StefanSalewski]

#[
proc newColumnView*(model: SelectionModel | MultiSelection | NoSelection | SingleSelection = nil): ColumnView =
  let gobj = gtk_column_view_new(if model.isNil: nil else: cast[ptr SelectionModel00](g_object_ref(model.impl)))
  let qdata = g_object_get_qdata(gobj, Quark)
  if qdata != nil:
    result = cast[type(result)](qdata)
    assert(result.impl == gobj)
  else:
    fnew(result, gtk4.finalizeGObject)
    result.impl = gobj
    GC_ref(result)
    discard g_object_ref_sink(result.impl)
    g_object_add_toggle_ref(result.impl, toggleNotify, addr(result[]))
    g_object_unref(result.impl)
    assert(g_object_get_qdata(result.impl, Quark) == nil)
    g_object_set_qdata(result.impl, Quark, addr(result[]))
]#

type
  A = ref object
    impl: pointer
    i: int

  B = ref object
    impl: pointer
    j: int

#proc t(x: A = nil) = # works
proc t(x: A | B = nil) =
  echo(if x == nil: "nil" else: $(cast[int](x.impl)))

proc main =
  var h: A
  t() # Error: cannot instantiate: 'T'
  t(h) # works
  t(x = nil) # Error: undeclared field: 'impl'

main()

[beef331]

nil without a type and no way to infer the type is typed to typeof(nil), so simply doing

type
  A = ref object
    impl: pointer
    i: int

  B = ref object
    impl: pointer
    j: int

#proc t(x: A = nil) = # works
proc t(x: A | B = A(nil)) =
  echo(if x == nil: "nil" else: $(cast[int](x.impl)))

proc main =
  var h: A
  t() # Error: cannot instantiate: 'T'
  t(h) # works
  t(x = B(nil)) # Error: undeclared field: 'impl'

main()

Solves the latter issue.

What you may want is:

proc t(x: A | B) =
  echo(if x == nil: "nil" else: $(cast[int](x.impl)))
  
proc t(x: typedesc[A | B]) =
  t(default(x))
# The folllowing can be used for the `nil` case.
t(A)
t(B)

[StefanSalewski]

Well, should be fixed, try

nimble uninstall gintro
nimble install gintro@#head