From e2546b70ca04d4263f7a5917815506e488b6920f Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Thu, 29 Jun 2023 18:32:58 +0300
Subject: [PATCH] Document uses_double_storage(). Refs #37.

---
 doc/variant2/changelog.adoc |  4 ++++
 doc/variant2/reference.adoc | 14 ++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/doc/variant2/changelog.adoc b/doc/variant2/changelog.adoc
index dd903ee..fc14105 100644
--- a/doc/variant2/changelog.adoc
+++ b/doc/variant2/changelog.adoc
@@ -8,6 +8,10 @@ https://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix: changelog_
 
+## Changes in 1.83.0
+
+* Added `uses_double_storage()`.
+
 ## Changes in 1.81.0
 
 * Added support for `boost::json::value_from` and `boost::json::value_to`.
diff --git a/doc/variant2/reference.adoc b/doc/variant2/reference.adoc
index beede7b..04bd748 100644
--- a/doc/variant2/reference.adoc
+++ b/doc/variant2/reference.adoc
@@ -250,6 +250,8 @@ public:
   constexpr bool valueless_by_exception() const noexcept;
   constexpr size_t index() const noexcept;
 
+  static constexpr bool uses_double_storage() noexcept;
+
   // swap
 
   void swap( variant& r ) noexcept( /*see below*/ );
@@ -570,6 +572,18 @@ constexpr size_t index() const noexcept;
 Returns:  ::
   The zero-based index of the active alternative.
 
+```
+static constexpr bool uses_double_storage() noexcept;
+```
+[none]
+* {blank}
++
+Returns:  ::
+  `true` if the variant uses double storage to meet the never valueless
+  guarantee because one of the alternatives is not nothrow move constructible,
+  and `false` otherwise.
+
+
 #### Swap
 
 ```