From c25a7544b8ae2171d8ac240089f3dd71cafc9a1c Mon Sep 17 00:00:00 2001
From: Pascal Menuet <pmenuet@libertysurf.fr>
Date: Fri, 14 Aug 2020 16:11:11 +0200
Subject: [PATCH] Fix finally with mutable lvalue invokable

---
 include/gsl/gsl_util  | 12 ++++--------
 tests/utils_tests.cpp | 22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index 585b3f9..ca733ac 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -52,6 +52,8 @@ template <class F>
 class final_action
 {
 public:
+    static_assert(!std::is_reference<F>::value && !std::is_const<F>::value && !std::is_volatile<F>::value, "Final_action should store its callable by value");
+
     explicit final_action(F f) noexcept : f_(std::move(f)) {}
 
     final_action(final_action&& other) noexcept : f_(std::move(other.f_)), invoke_(std::exchange(other.invoke_, false)) {}
@@ -73,15 +75,9 @@ private:
 
 // finally() - convenience function to generate a final_action
 template <class F>
-GSL_NODISCARD final_action<F> finally(const F& f) noexcept
+GSL_NODISCARD final_action<typename std::remove_cv<typename std::remove_reference<F>::type>::type> finally(F&& f) noexcept
 {
-    return final_action<F>(f);
-}
-
-template <class F>
-GSL_NODISCARD final_action<F> finally(F&& f) noexcept
-{
-    return final_action<F>(std::forward<F>(f));
+    return final_action<typename std::remove_cv<typename std::remove_reference<F>::type>::type>(std::forward<F>(f));
 }
 
 // narrow_cast(): a searchable way to do narrowing casts of values
diff --git a/tests/utils_tests.cpp b/tests/utils_tests.cpp
index fae48f5..430788e 100644
--- a/tests/utils_tests.cpp
+++ b/tests/utils_tests.cpp
@@ -70,6 +70,28 @@ TEST(utils_tests, finally_lambda_move)
     EXPECT_TRUE(i == 1);
 }
 
+TEST(utils_tests, finally_const_lvalue_lambda)
+{
+    int i = 0;
+    {
+        const auto const_lvalue_lambda = [&]() { f(i); };
+        auto _ = finally(const_lvalue_lambda);
+        EXPECT_TRUE(i == 0);
+    }
+    EXPECT_TRUE(i == 1);
+}
+
+TEST(utils_tests, finally_mutable_lvalue_lambda)
+{
+    int i = 0;
+    {
+        auto mutable_lvalue_lambda = [&]() { f(i); };
+        auto _ = finally(mutable_lvalue_lambda);
+        EXPECT_TRUE(i == 0);
+    }
+    EXPECT_TRUE(i == 1);
+}
+
 TEST(utils_tests, finally_function_with_bind)
 {
     int i = 0;