singleton.h

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#pragma once
 
#include <mutex>
 
#undef CUTL_COPY_AND_ASSIGN
#define CUTL_COPY_AND_ASSIGN(classname) \
 classname(const classname &) = delete; \
 classname &operator=(const classname &) = delete;
 
#undef CUTL_SINGLETON_PTR
#define CUTL_SINGLETON_PTR(classname) \
public: \
 static classname *get_instance(bool create_if_needed = true) \
 { \
 static classname *obj = nullptr; \
 if (!obj && create_if_needed) \
 { \
 static std::once_flag flag; \
 std::call_once(flag, [&] { obj = new (std::nothrow) classname(); }); \
 } \
 return obj; \
 } \
 ~classname(); \
 \
private: \
 classname(); \
 CUTL_COPY_AND_ASSIGN(classname)
 
#undef CUTL_SINGLETON_PTR_DEFAULT_CTOR
#define CUTL_SINGLETON_PTR_DEFAULT_CTOR(classname) \
public: \
 static classname *get_instance(bool create_if_needed = true) \
 { \
 static classname *obj = nullptr; \
 if (!obj && create_if_needed) \
 { \
 static std::once_flag flag; \
 std::call_once(flag, [&] { obj = new (std::nothrow) classname(); }); \
 } \
 return obj; \
 } \
 ~classname(); \
 \
private: \
 classname() = default; \
 CUTL_COPY_AND_ASSIGN(classname)
 
#undef CUTL_SINGLETON_REF
#define CUTL_SINGLETON_REF(classname) \
public: \
 static classname &get_instance(bool create_if_needed = true) \
 { \
 static classname obj; \
 return obj; \
 } \
 ~classname(); \
 \
private: \
 classname(); \
 CUTL_COPY_AND_ASSIGN(classname)
 
#undef CUTL_SINGLETON_REF_DEFAULT_CTOR
#define CUTL_SINGLETON_REF_DEFAULT_CTOR(classname) \
public: \
 static classname &get_instance(bool create_if_needed = true) \
 { \
 static classname obj; \
 return obj; \
 } \
 ~classname(); \
 \
private: \
 classname() = default; \
 CUTL_COPY_AND_ASSIGN(classname)