From 020ddc40c5d807513b01767dace2e607ceae9055 Mon Sep 17 00:00:00 2001
From: Herb Sutter <herb.sutter@gmail.com>
Date: Wed, 24 Feb 2021 16:49:57 -0800
Subject: [PATCH] Fine, make it move-constructible (only)

To satisfy some compilers.
And might as well reinstate that test case.
---
 include/gsl/util      | 10 ++++++++--
 tests/utils_tests.cpp | 19 +++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/include/gsl/util b/include/gsl/util
index ebaeef6..5e9256f 100644
--- a/include/gsl/util
+++ b/include/gsl/util
@@ -52,14 +52,20 @@ template <class F>
 class final_action
 {
 public:
-    explicit final_action(F f_) : f(f_) { }
-    ~final_action() { f(); }
+    explicit final_action(F f_) : f(std::move(f_)) { }
+    ~final_action() { if (invoke) f(); }
+
+    final_action(final_action&& other)
+        : f(std::move(other.f)), invoke(std::exchange(other.invoke, false))
+    { }
 
     final_action(const final_action& rhs) = delete;
     final_action& operator=(const final_action&) = delete;
+    final_action& operator=(final_action&& other) = delete;
 
 private:
     F f;
+    bool invoke = true;
 };
 
 // finally() - convenience function to generate a final_action
diff --git a/tests/utils_tests.cpp b/tests/utils_tests.cpp
index 705f384..74dc990 100644
--- a/tests/utils_tests.cpp
+++ b/tests/utils_tests.cpp
@@ -51,6 +51,25 @@ TEST(utils_tests, finally_lambda)
     EXPECT_TRUE(i == 1);
 }
 
+TEST(utils_tests, finally_lambda_move)
+{
+    int i = 0;
+    {
+        auto _1 = finally([&]() { f(i); });
+        {
+            auto _2 = std::move(_1);
+            EXPECT_TRUE(i == 0);
+        }
+        EXPECT_TRUE(i == 1);
+        {
+            auto _2 = std::move(_1);
+            EXPECT_TRUE(i == 1);
+        }
+        EXPECT_TRUE(i == 1);
+    }
+    EXPECT_TRUE(i == 1);
+}
+
 TEST(utils_tests, finally_const_lvalue_lambda)
 {
     int i = 0;