tempbottle · August 29, 2015 14:07 · Jun 23, 2013
diff --git a/singleton.hpp b/singleton.hpp
@@ -0,0 +1,121 @@
+//
+//  __SINGLETON_HPP__
+//
+// The MIT License (MIT)
+
+// Copyright (c) <2013> <Jiang Bian [email protected]>
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+// Usage:
+//   class Foo : public Singleton<Foo> {
+//       friend class Singleton<Foo>;
+
+//   private:
+
+//       Foo(const std::string& hello) : hello_(hello)  {
+//           std::cout << hello << std::endl;
+//       }
+
+//       Foo() : hello_(nullptr) {
+//           std::cout << "Foo()" << std::endl;
+//       }
+
+//       const std::string& hello_;
+//   };
+
+//   int main(int, const char**) {
+//     const std::string hello("hello world");
+//     Foo::getInstance(hello);
+//     Foo::getInstance();
+//   }
+
+#ifndef __SINGLETON_HPP__
+#define __SINGLETON_HPP__
+
+#include <mutex>
+#include <functional>
+#include <memory>
+#include <utility>
+
+using std::call_once;
+using std::once_flag;
+
+// This is from boost/utility.hpp
+// if you don't mind having dependency on boost, get rid of this, and replace it with boost::noncopyable
+namespace noncopyable_  // protection from unintended ADL
+{
+  class noncopyable
+  {
+   protected:
+      noncopyable() {}
+      ~noncopyable() {}
+   private:  // emphasize the following members are private
+      noncopyable( const noncopyable& );
+      const noncopyable& operator=( const noncopyable& );
+  };
+}
+
+typedef noncopyable_::noncopyable noncopyable;
+
+
+template <class T>
+class Singleton : private noncopyable {
+  public:
+    template <typename... Args>
+    static T& getInstance(Args&&... args) {
+
+      call_once(
+        get_once_flag(),
+        [] (Args&&... args) {
+          instance_.reset(new T(std::forward<Args>(args)...));
+        }, std::forward<Args>(args)...);
+      /*
+      c++11 standard does specify the following syntax to be valid... but it is not supported by gcc-4.8 yet.
+      Final Committee Draft, section 5.1.2.23:
+      A capture followed by an ellipsis is a pack expansion (14.5.3). [ Example:
+
+      template<class... Args> void f(Args... args) {
+          auto lm = [&, args...] { return g(args...); }; lm();
+      }
+      — end example ]
+      call_once(
+        get_once_flag(),
+        [&, args...] () {
+          instance_.reset(new T(std::forward<Args>(args)...));
+        });
+      */
+      return *instance_.get();
+    }
+
+  protected:
+    explicit Singleton<T>() {}
+    ~Singleton<T>() {}
+
+  private:
+    static std::unique_ptr<T> instance_;
+    static once_flag& get_once_flag() {
+      static once_flag once_;
+      return once_;
+    }
+};
+
+template<class T> std::unique_ptr<T> Singleton<T>::instance_ = nullptr;
+
+#endif
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