From 3048a4ba85c58596eae97552982dba4053b2e4b2 Mon Sep 17 00:00:00 2001
From: flywind <xzsflywind@gmail.com>
Date: Sun, 7 Feb 2021 22:52:49 +0800
Subject: [PATCH] close #15767

---
 lib/pure/collections/sets.nim | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/pure/collections/sets.nim b/lib/pure/collections/sets.nim
index a9df9ded8847a..5cf72863b6fe6 100644
--- a/lib/pure/collections/sets.nim
+++ b/lib/pure/collections/sets.nim
@@ -241,8 +241,11 @@ iterator items*[A](s: HashSet[A]): A =
   ##   assert a.len == 2
   ##   echo b
   ##   # --> {(a: 1, b: 3), (a: 0, b: 4)}
+  let length = s.len
   for h in 0 .. high(s.data):
-    if isFilled(s.data[h].hcode): yield s.data[h].key
+    if isFilled(s.data[h].hcode):
+      yield s.data[h].key
+      assert(len(s) == length, "the length of the HashSet changed while iterating over it")
 
 proc containsOrIncl*[A](s: var HashSet[A], key: A): bool =
   ## Includes `key` in the set `s` and tells if `key` was already in `s`.
@@ -901,8 +904,10 @@ iterator items*[A](s: OrderedSet[A]): A =
   ##   # --> Got 5
   ##   # --> Got 8
   ##   # --> Got 4
+  let length = s.len
   forAllOrderedPairs:
     yield s.data[h].key
+    assert(len(s) == length, "the length of the OrderedSet changed while iterating over it")
 
 iterator pairs*[A](s: OrderedSet[A]): tuple[a: int, b: A] =
   ## Iterates through (position, value) tuples of OrderedSet `s`.
@@ -913,5 +918,7 @@ iterator pairs*[A](s: OrderedSet[A]): tuple[a: int, b: A] =
       p.add(x)
     assert p == @[(0, 'a'), (1, 'b'), (2, 'r'), (3, 'c'), (4, 'd')]
 
+  let length = s.len
   forAllOrderedPairs:
     yield (idx, s.data[h].key)
+    assert(len(s) == length, "the length of the OrderedSet changed while iterating over it")