util/ScopeExit: new utility library

Makefile.am

@@ -359,6 +359,7 @@ libutil_a_SOURCES = \
 	src/util/Clamp.hxx \
 	src/util/Alloc.cxx src/util/Alloc.hxx \
 	src/util/VarSize.hxx \
+	src/util/ScopeExit.hxx \
 	src/util/Error.cxx src/util/Error.hxx \
 	src/util/Domain.hxx \
 	src/util/ReusableArray.hxx \

src/util/ScopeExit.hxx

+/*
+ * Copyright (C) 2015 Max Kellermann <max@duempel.org>
+ *
+ * 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.
+ *
+ * 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
+ * FOUNDATION 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.
+ */
+
+#ifndef SCOPE_EXIT_HXX
+#define SCOPE_EXIT_HXX
+
+#include "Compiler.h"
+
+#include <utility>
+
+/**
+ * Internal class.  Do not use directly.
+ */
+template<typename F>
+class ScopeExitGuard : F {
+	bool enabled = true;
+
+public:
+	explicit ScopeExitGuard(F &&f):F(std::forward<F>(f)) {}
+
+	ScopeExitGuard(ScopeExitGuard &&src)
+		:F(std::move(src)) {
+		src.enabled = false;
+	}
+
+	~ScopeExitGuard() {
+		if (enabled)
+			F::operator()();
+	}
+
+	ScopeExitGuard(const ScopeExitGuard &) = delete;
+	ScopeExitGuard &operator=(const ScopeExitGuard &) = delete;
+};
+
+/**
+ * Internal class.  Do not use directly.
+ */
+struct ScopeExitTag {
+	/* this operator is a trick so we don't need to close
+	   parantheses at the end of the expression AtScopeExit()
+	   call */
+	template<typename F>
+	ScopeExitGuard<F> operator+(F &&f) {
+		return ScopeExitGuard<F>(std::forward<F>(f));
+	}
+};
+
+#define ScopeExitCat(a, b) a ## b
+#define ScopeExitName(line) ScopeExitCat(at_scope_exit_, line)
+
+/**
+ * Call the block after this macro at the end of the current scope.
+ * Parameters are lambda captures.
+ *
+ * This is exception-safe, however the given code block must not throw
+ * exceptions.
+ *
+ * This attempts to be a better boost/scope_exit.hpp, without all of
+ * Boost's compile-time and runtime bloat.
+ */
+#define AtScopeExit(...) auto ScopeExitName(__LINE__) = ScopeExitTag() + [__VA_ARGS__]()
+
+#endif