From 568c557dde1dbd078a5b4c5b55a95402fcd6c936 Mon Sep 17 00:00:00 2001
From: david33101 <87750900+david33101@users.noreply.github.com>
Date: Wed, 21 Jul 2021 15:31:45 +0800
Subject: [PATCH] Update ex13_31.h

Function swap(HasPtr&, HasPtr&) is actually never used. The notice is printed because '=' is called. This happens maybe because 'sort'  doesn't call swap(HasPtr&, HasPtr&) at all in this situation.
---
 ch13/ex13_31.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/ch13/ex13_31.h b/ch13/ex13_31.h
index 1d21d6da..7bfabb79 100644
--- a/ch13/ex13_31.h
+++ b/ch13/ex13_31.h
@@ -50,6 +50,9 @@ void swap(HasPtr& lhs, HasPtr& rhs)
 {
     lhs.swap(rhs);
 }
+//Function swap(HasPtr&, HasPtr&) is actually never used. The notice is printed because '=' is called, and 'sort' doesn't call swap(HasPtr&, HasPtr&) at all. 
+//I saw a comment that might be the reason:
+//swap(HasPtr&, HasPtr&) is used in quicksort, but 'sort' won't use quicksort when there are not enough elements in the container(insertionsort is used instead).
 
 bool operator<(const HasPtr& lhs, const HasPtr& rhs)
 {