From 2f8501074ea5f4c6fe650b7c29115e5b0d476bd7 Mon Sep 17 00:00:00 2001
From: Fedor Alekseev <github@falekseev.com>
Date: Thu, 23 Oct 2025 15:10:22 +0200
Subject: [PATCH 1/2] Avoid constructing temporary T in make_box

---
 include/function2/function2.hpp | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/function2/function2.hpp b/include/function2/function2.hpp
index 6453f70..d272d93 100644
--- a/include/function2/function2.hpp
+++ b/include/function2/function2.hpp
@@ -376,7 +376,11 @@ struct box : private Allocator {
 
   T value_;
 
-  explicit box(T value, Allocator allocator_)
+  explicit box(const T& value, Allocator allocator_)
+      : Allocator(std::move(allocator_)), value_(value) {
+  }
+
+  explicit box(T&& value, Allocator allocator_)
       : Allocator(std::move(allocator_)), value_(std::move(value)) {
   }
 
@@ -392,7 +396,11 @@ struct box<false, T, Allocator> : private Allocator {
 
   T value_;
 
-  explicit box(T value, Allocator allocator_)
+  explicit box(const T& value, Allocator allocator_)
+      : Allocator(std::move(allocator_)), value_(std::move(value)) {
+  }
+
+  explicit box(T&& value, Allocator allocator_)
       : Allocator(std::move(allocator_)), value_(std::move(value)) {
   }
 

From da75c3be8d5948901e72bfa0e1cd5bcf27dbc710 Mon Sep 17 00:00:00 2001
From: Fedor Alekseev <github@falekseev.com>
Date: Thu, 23 Oct 2025 15:10:29 +0200
Subject: [PATCH 2/2] Add a regression test

---
 include/function2/function2.hpp |  2 +-
 test/regressions.cpp            | 41 +++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/include/function2/function2.hpp b/include/function2/function2.hpp
index d272d93..5ab18d7 100644
--- a/include/function2/function2.hpp
+++ b/include/function2/function2.hpp
@@ -397,7 +397,7 @@ struct box<false, T, Allocator> : private Allocator {
   T value_;
 
   explicit box(const T& value, Allocator allocator_)
-      : Allocator(std::move(allocator_)), value_(std::move(value)) {
+      : Allocator(std::move(allocator_)), value_(value) {
   }
 
   explicit box(T&& value, Allocator allocator_)
diff --git a/test/regressions.cpp b/test/regressions.cpp
index 54ef428..63871ee 100644
--- a/test/regressions.cpp
+++ b/test/regressions.cpp
@@ -6,6 +6,7 @@
 
 #include <memory>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "function2-test.hpp"
@@ -261,3 +262,43 @@ TYPED_TEST(AllReferenceRetConstructTests, reference_returns_not_buildable) {
   ref_obj& ref = left();
   ASSERT_EQ(ref.data(), 8373827);
 }
+
+/// Functor which counts the number of times it has been copied or moved
+class CopyAndMoveCountFunctor {
+  int copy_count = 0;
+  int move_count = 0;
+
+public:
+  CopyAndMoveCountFunctor() = default;
+
+  CopyAndMoveCountFunctor(const CopyAndMoveCountFunctor& that) {
+    *this = that;
+  }
+
+  CopyAndMoveCountFunctor& operator=(const CopyAndMoveCountFunctor& that) {
+    copy_count = that.copy_count + 1;
+    move_count = that.move_count;
+    return *this;
+  }
+
+  CopyAndMoveCountFunctor(CopyAndMoveCountFunctor&& that) {
+    *this = std::move(that);
+  }
+
+  CopyAndMoveCountFunctor& operator=(CopyAndMoveCountFunctor&& that) {
+    copy_count = that.copy_count;
+    move_count = that.move_count + 1;
+    return *this;
+  }
+
+  ~CopyAndMoveCountFunctor() = default;
+
+  std::pair<int, int> operator()() const {
+    return std::make_pair(copy_count, move_count);
+  }
+};
+
+TEST(regression_tests, no_extra_move_during_construction) {
+  fu2::function<std::pair<int, int>()> f(CopyAndMoveCountFunctor{});
+  ASSERT_EQ(f(), std::make_pair(0, 2));
+}