Add a helper for generic scope guards.

Author: dvander

amtl/am-raii.h

@@ -1,4 +1,4 @@
-// vim: set sts=8 ts=2 sw=2 tw=99 et:
+// vim: set sts=4 ts=8 sw=4 tw=99 et:
 //
 // Copyright (C) 2013-2014, David Anderson and AlliedModders LLC
 // All rights reserved.
@@ -30,6 +30,8 @@
 #ifndef _include_amtl_am_raii_h_
 #define _include_amtl_am_raii_h_
 
+#include <utility>
+
 namespace ke {
 
 template <typename T>
@@ -71,6 +73,48 @@ class StackLinked
     T* prev_;
 };
 
+template <typename T>
+class ScopeGuard
+{
+  public:
+    ScopeGuard(T&& callback) noexcept
+      : callback_(std::forward<T>(callback)),
+        cancelled_(false)
+    {}
+    ScopeGuard(ScopeGuard&& other) noexcept
+      : callback_(std::move(other.callback_)),
+        cancelled_(other.cancelled_)
+    {
+        other.cancel();
+    }
+
+    ~ScopeGuard() {
+        if (!cancelled_)
+            callback_();
+    }
+
+    void cancel() {
+        cancelled_ = true;
+    }
+
+  private:
+    ScopeGuard() = delete;
+    ScopeGuard(const ScopeGuard&) = delete;
+
+    void operator=(const ScopeGuard&) = delete;
+    void operator=(ScopeGuard&&) = delete;
+
+  private:
+    T callback_;
+    bool cancelled_;
+};
+
+template <typename T>
+ScopeGuard<T> MakeScopeGuard(T&& callback)
+{
+    return ScopeGuard<T>(std::forward<T>(callback));
+}
+
 template <typename T>
 T
 ReturnAndVoid(T& t)

tests/AMBuild.tests

@@ -53,6 +53,7 @@ binary.sources += [
   'test-inlinelist.cpp',
   'test-priority-queue.cpp',
   'test-refcounting.cpp',
+  'test-raii.cpp',
   'test-string.cpp',
   'test-system.cpp',
   'test-threadlocal-threaded.cpp',

tests/test-raii.cpp

@@ -0,0 +1,67 @@
+// vim: set sts=4 ts=8 sw=4 tw=99 et:
+//
+// Copyright (C) 2021 AlliedModders LLC
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//  * Redistributions of source code must retain the above copyright notice, this
+//    list of conditions and the following disclaimer.
+//  * Redistributions in binary form must reproduce the above copyright notice,
+//    this list of conditions and the following disclaimer in the documentation
+//    and/or other materials provided with the distribution.
+//  * Neither the name of AlliedModders LLC nor the names of its contributors
+//    may be used to endorse or promote products derived from this software
+//    without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+
+#include <amtl/am-raii.h>
+#include <gtest/gtest.h>
+#include "runner.h"
+
+using namespace ke;
+
+TEST(ScopeGuard, Invoke)
+{
+    int invokes = 0;
+
+    {
+        auto guard1 = MakeScopeGuard([&]() -> void {
+            invokes++;
+        });
+
+        {
+            auto guard2 = MakeScopeGuard([&]() -> void {
+                invokes++;
+            });
+        }
+        ASSERT_EQ(invokes, 1);
+    }
+    ASSERT_EQ(invokes, 2);
+}
+
+TEST(ScopeGuard, Cancel)
+{
+    int invokes = 0;
+
+    {
+        auto guard1 = MakeScopeGuard([&]() -> void {
+            invokes++;
+        });
+
+        guard1.cancel();
+    }
+    ASSERT_EQ(invokes, 0);
+}