fix #587

tests/metatype/udtcmanual.nim

@@ -0,0 +1,43 @@
+discard """
+  output: '''1
+2
+3
+4
+5
+6
+a
+b
+t
+e
+s
+t
+'''
+"""
+
+template accept(e: expr) =
+  static: assert compiles(e)
+
+template reject(e: expr) =
+  static: assert(not compiles(e))
+
+type
+  Container[T] = generic C
+    C.len is Ordinal
+    items(c) is iterator
+    for value in C:
+      value.type is T
+
+proc takesIntContainer(c: Container[int]) =
+  for e in c: echo e
+
+takesIntContainer(@[1, 2, 3])
+reject takesIntContainer(@["x", "y"])
+
+proc takesContainer(c: Container) =
+  for e in c: echo e
+
+takesContainer(@[4, 5, 6])
+takesContainer(@["a", "b"])
+takesContainer "test"
+reject takesContainer(10)
+