From 7820e74b0d4ac410698331f8977fb2b8e0df4416 Mon Sep 17 00:00:00 2001
From: Enrico Maria De Angelis <enricomaria.dean6elis@gmail.com>
Date: Tue, 10 Sep 2024 18:14:59 +0100
Subject: [PATCH] Update CppCoreGuidelines.md

Addressing the issue #2205 I opened myself.

I can't see why not contributing.
---
 CppCoreGuidelines.md | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md
index 8589d784b..a179b00ff 100644
--- a/CppCoreGuidelines.md
+++ b/CppCoreGuidelines.md
@@ -11165,6 +11165,16 @@ Use plain `{}`-initialization unless you specifically want to disable explicit c
         // ...
     }
 
+##### Exception
+
+For container-like types whose element type can be initialized from an instance of that very container
+type iteself, e.g. `std::any` or a template parameter `T` of a template type having a constructor accepting `T`,
+use `()` to avoid erroneously constructing a nested container:
+
+    vector<any> v{1,2,3};
+    vector<any> u{v}; // most likely unintended: u has 1 element of type any, which contains v
+    vector<any> w(v); // w is a copy of v
+
 **See also**: [Discussion](#???)
 
 ##### Enforcement