Sometimes you need to share data between instances, but you need that data to be accessed externally, automatically created when needed, and destroyed when not needed anymore.<\/p>\n
You can use something\u00a0like this:<\/p>\n
\r\ntemplate<typename T>\r\nstd::shared_ptr<T> getSharedData()\r\n{\r\n static std::mutex mtx;\r\n static std::weak_ptr<T> ptr;\r\n std::lock_guard<std::mutex> lk(mtx);\r\n auto p = ptr.lock();\r\n if (p)\r\n return p;\r\n p = std::make_shared<T>();\r\n ptr = p;\r\n return p;\r\n}\r\n<\/pre>\nThis way you can have instances getting a strong reference to that data, creating it if necessary.<\/p>\n
\r\nstruct FooSharedData \r\n{\r\n \/\/ ... details here\r\n};\r\n\r\nclass Foo\r\n{\r\npublic:\r\n Foo() : m_shared(getSharedData<FooSharedData>()) { }\r\nprivate:\r\n std::shared_ptr<FooSharedData> m_shared;\r\n};\r\n\r\nvoid someFunction()\r\n{\r\n {\r\n Foo a; \/\/ Will create the FooSharedData instance\r\n Foo b; \/\/ Will grab the existing FooSharedData instance\r\n \/\/ Can access it externally too\r\n auto data = getSharedData<FooSharedData>();\r\n }\r\n \/\/ At this point, there are no more strong references to the FooSharedData instance,\r\n \/\/ so it gets deleted\r\n\r\n \/\/ This will recreate a FooSharedData instance, since the previous one was destroyed\r\n Foo c;\r\n};\r\n<\/pre>\nLicense<\/h3>\n