fixes #554, fixes #179

tests/compile/tinheritref.nim

@@ -0,0 +1,27 @@
+discard """
+  output: "23"
+"""
+
+# bug #554, #179
+
+type T[E] =
+  ref object
+    elem: E
+
+var ob: T[int]
+
+ob = T[int](elem: 23)
+echo ob.elem
+
+type
+  TTreeIteratorA* = ref object {.inheritable.}
+
+  TKeysIteratorA* = ref object of TTreeIteratorA  #compiles
+
+  TTreeIterator* [T,D] = ref object {.inheritable.}
+
+  TKeysIterator* [T,D] = ref object of TTreeIterator[T,D]  #this not
+  
+var
+  it: TKeysIterator[int, string] = nil
+