fixes #10912 (#11317)

* fixes #10912

* update the tutorial examples

tests/method/tsingle_methods.nim

@@ -0,0 +1,48 @@
+discard """
+  cmd: "nim c --multimethods:off $file"
+  output: '''base
+base
+base
+base
+base
+base
+'''
+"""
+
+# bug #10912
+
+type
+  X = ref object of RootObj
+
+type
+  A* = ref object of RootObj
+  B* = ref object of A
+  C* = ref object of A
+  D* = ref object of A
+  E* = ref object of A
+  F* = ref object of A
+
+method resolve(self: var X, stmt: A) {.base.} = echo "base"
+
+proc resolveSeq*(self: var X, statements: seq[A]) =
+  for statement in statements:
+    resolve(self, statement)
+
+method resolve(self: var X, stmt: B) =
+  echo "B"
+
+method resolve(self: var X, stmt: D) =
+  echo "D"
+
+method resolve(self: var X, stmt: E) =
+  echo "E"
+
+method resolve(self: var X, stmt: C) =
+  echo "C"
+
+method resolve(self: var X, stmt: F) =
+  echo "F"
+
+var x = X()
+var a = @[A(), B(), C(), D(), E(), F()]
+resolveSeq(x, a)