util/Manual: new template class

Makefile.am

@@ -301,6 +301,7 @@ endif
 # Generic utility library
 
 libutil_a_SOURCES = \
+	src/util/Manual.hxx \
 	src/util/RefCount.hxx \
 	src/util/fifo_buffer.c src/util/fifo_buffer.h \
 	src/util/growing_fifo.c src/util/growing_fifo.h \

src/util/Manual.hxx

+/*
+ * Copyright (C) 2013 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 MPD_MANUAL_HXX
+#define MPD_MANUAL_HXX
+
+#include "gcc.h"
+
+#include <new>
+
+#if !defined(__clang__) && __GNUC__ && !GCC_CHECK_VERSION(4,8)
+#include <type_traits>
+#endif
+
+#include <assert.h>
+
+/**
+ * Container for an object that gets constructed and destructed
+ * manually.  The object is constructed in-place, and therefore
+ * without allocation overhead.  It can be constructed and destructed
+ * repeatedly.
+ */
+template<class T>
+class Manual {
+#if !defined(__clang__) && __GNUC__ && !GCC_CHECK_VERSION(4,8)
+	/* no alignas() on gcc < 4.8: apply worst-case fallback */
+	__attribute__((aligned(8)))
+#else
+	alignas(T)
+#endif
+	char data[sizeof(T)];
+
+#ifndef NDEBUG
+	bool initialized;
+#endif
+
+public:
+#ifndef NDEBUG
+	Manual():initialized(false) {}
+	~Manual() {
+		assert(!initialized);
+	}
+#endif
+
+	template<typename... Args>
+	void Construct(Args&&... args) {
+		assert(!initialized);
+
+		void *p = data;
+		new(p) T(std::forward<Args>(args)...);
+
+#ifndef NDEBUG
+		initialized = true;
+#endif
+	}
+
+	void Destruct() {
+		assert(initialized);
+
+		T *t = (T *)data;
+		t->T::~T();
+
+#ifndef NDEBUG
+		initialized = false;
+#endif
+	}
+
+	operator T &() {
+		return *(T *)data;
+	}
+
+	operator const T &() const {
+		return *(const T *)data;
+	}
+
+	T *operator->() {
+		return (T *)data;
+	}
+
+	const T *operator->() const {
+		return (T *)data;
+	}
+};
+
+#endif