From fa3babf4e686ca98f5fb3b3d1ea478a7b23bc532 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Wed, 25 Feb 2026 14:10:14 +0200
Subject: [PATCH] Add unwrap_and_construct

---
 include/boost/system/unwrap_and_invoke.hpp |  22 +++++
 test/CMakeLists.txt                        |   2 +
 test/Jamfile.v2                            |   2 +
 test/unwrap_and_construct.cpp              | 109 +++++++++++++++++++++
 4 files changed, 135 insertions(+)
 create mode 100644 test/unwrap_and_construct.cpp

diff --git a/include/boost/system/unwrap_and_invoke.hpp b/include/boost/system/unwrap_and_invoke.hpp
index 5b0d1d4..ff726b7 100644
--- a/include/boost/system/unwrap_and_invoke.hpp
+++ b/include/boost/system/unwrap_and_invoke.hpp
@@ -81,6 +81,28 @@ auto unwrap_and_invoke( F&& f, A&&... a ) -> result<R, E>
     return compat::invoke( std::forward<F>(f), detail::invoke_unwrap( std::forward<A>(a) )... );
 }
 
+// unwrap_and_construct
+
+namespace detail
+{
+
+template<class T> struct construct
+{
+    template<class... A> T operator()( A&&... a ) const
+    {
+        return T( std::forward<A>(a)... );
+    }
+};
+
+} // namespace detail
+
+template<class T, class... A>
+auto unwrap_and_construct( A&&... a )
+-> decltype( unwrap_and_invoke( detail::construct<T>(), std::forward<A>(a)... ) )
+{
+    return unwrap_and_invoke( detail::construct<T>(), std::forward<A>(a)... );
+}
+
 } // namespace system
 } // namespace boost
 
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 0d2bab7..865fc29 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -190,3 +190,5 @@ boost_test(TYPE run SOURCES result_unsafe_value_access2.cpp)
 
 boost_test(TYPE run SOURCES unwrap_and_invoke.cpp)
 boost_test(TYPE run SOURCES unwrap_and_invoke2.cpp)
+
+boost_test(TYPE run SOURCES unwrap_and_construct.cpp)
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index dc76e48..9ff4b15 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -223,3 +223,5 @@ run result_unsafe_value_access2.cpp ;
 
 run unwrap_and_invoke.cpp ;
 run unwrap_and_invoke2.cpp ;
+
+run unwrap_and_construct.cpp ;
diff --git a/test/unwrap_and_construct.cpp b/test/unwrap_and_construct.cpp
new file mode 100644
index 0000000..43f3a55
--- /dev/null
+++ b/test/unwrap_and_construct.cpp
@@ -0,0 +1,109 @@
+// Copyright 2026 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/unwrap_and_invoke.hpp>
+#include <boost/system/result.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+
+using namespace boost::system;
+
+struct X
+{
+    int v;
+};
+
+struct Y
+{
+    int v;
+
+    explicit Y( X a1 = {}, X a2 = {}, X a3 = {}, X a4 = {} ): v( a1.v + a2.v + a3.v + a4.v )
+    {
+    }
+};
+
+struct E
+{
+    int w;
+};
+
+int main()
+{
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( E{1} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 1 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ) );
+        BOOST_TEST( r ) && BOOST_TEST_EQ( r.unsafe_value().v, 1 );
+    }
+
+    //
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( E{1} ), result<X, E>( E{2} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 1 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( E{2} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 2 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( X{2} ) );
+        BOOST_TEST( r ) && BOOST_TEST_EQ( r.unsafe_value().v, 3 );
+    }
+
+    //
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( E{1} ), result<X, E>( E{2} ), result<X, E>( E{3} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 1 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( E{2} ), result<X, E>( E{3} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 2 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( X{2} ), result<X, E>( E{3} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 3 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( X{2} ), result<X, E>( X{3} ) );
+        BOOST_TEST( r ) && BOOST_TEST_EQ( r.unsafe_value().v, 6 );
+    }
+
+    //
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( E{1} ), result<X, E>( E{2} ), result<X, E>( E{3} ), result<X, E>( E{4} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 1 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( E{2} ), result<X, E>( E{3} ), result<X, E>( E{4} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 2 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( X{2} ), result<X, E>( E{3} ), result<X, E>( E{4} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 3 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( X{2} ), result<X, E>( X{3} ), result<X, E>( E{4} ) );
+        BOOST_TEST( !r ) && BOOST_TEST_EQ( r.error().w, 4 );
+    }
+
+    {
+        auto r = unwrap_and_construct<Y>( result<X, E>( X{1} ), result<X, E>( X{2} ), result<X, E>( X{3} ), result<X, E>( X{4} ) );
+        BOOST_TEST( r ) && BOOST_TEST_EQ( r.unsafe_value().v, 10 );
+    }
+
+    return boost::report_errors();
+}