From befd1530984489781bc0b7283f82898734928ff2 Mon Sep 17 00:00:00 2001
From: Camelid <camelidcamel@gmail.com>
Date: Sat, 9 Jan 2021 12:35:47 -0800
Subject: [PATCH] Add comment to `Vec::truncate` explaining `>` vs `>=`
Hopefully this will prevent people from continuing to ask about this
over and over again :)
See [this Zulip discussion][1] for more.
[1]: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Vec.3A.3Atruncate.20implementation
---
library/alloc/src/vec/mod.rs | 3 +++
1 file changed, 3 insertions(+)
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 2a83eb33fe3..1ca194c3361 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -990,6 +990,9 @@ impl<T, A: Allocator> Vec<T, A> {
// such that no value will be dropped twice in case `drop_in_place`
// were to panic once (if it panics twice, the program aborts).
unsafe {
+ // Note: It's intentional that this is `>` and not `>=`.
+ // Changing it to `>=` has negative performance
+ // implications in some cases. See #78884 for more.
if len > self.len {
return;
}