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Hi all, I'm writing some callback implementation in C++. I have an abstract callback class, let's say: /** Abstract callback class. */ class callback { public: /** Executes the callback. */ void call() { do_call(); }; protected: /** Callback call implementation specific to derived callback. */ virtual void do_call() = 0; }; Each callback I create (accepting single-argument functions, double-argument functions...) is created as a mixin using one of the following: /** Makes the callback a single-argument callback. */ template <typename T> class singleArgumentCallback { protected: /** Callback argument. */ T arg; public: /** Constructor. */ singleArgumentCallback(T arg): arg(arg) { } }; /** Makes the callback a double-argument callback. */ template <typename T, typename V> class doubleArgumentCallback { protected: /** Callback argument 1. */ T arg1; /** Callback argument 2. */ V arg2; public: /** Constructor. */ doubleArgumentCallback(T arg1, V arg2): arg1(arg1), arg2(arg2) { } }; For example, a single-arg function callback would look like this: /** Single-arg callbacks. */ template <typename T> class singleArgFunctionCallback: public callback, protected singleArgumentCallback<T> { /** Callback. */ void (*callbackMethod)(T arg); public: /** Constructor. */ singleArgFunctionCallback(void (*callback)(T), T argument): singleArgumentCallback<T>(argument), callbackMethod(callback) { } protected: void do_call() { this->callbackMethod(this->arg); } }; For user convenience, I'd like to have a method that creates a callback without having the user think about details, so that one can call (this interface is not subject to change, unfortunately): void test3(float x) { std::cout << x << std::endl; } void test5(const std::string& s) { std::cout << s << std::endl; } make_callback(&test3, 12.0f)->call(); make_callback(&test5, "oh hai!")->call(); My current implementation of make_callback(...) is as follows: /** Creates a callback object. */ template <typename T, typename U> callback* make_callback( void (*callbackMethod)(T), U argument) { return new singleArgFunctionCallback<T>(callbackMethod, argument); } Unfortunately, when I call make_callback(&test5, "oh hai!")->call(); I get an empty string on the standard output. I believe the problem is that the reference gets out of scope after callback initialization. I tried using pointers and references, but it's impossible to have a pointer/reference to reference, so I failed. The only solution I had was to forbid substituting reference type as T (for example, T cannot be std::string&) but that's a sad solution since I have to create another singleArgCallbackAcceptingReference class accepting a function pointer with following signature: void (*callbackMethod)(T& arg); thus, my code gets duplicated 2^n times, where n is the number of arguments of a callback function. Does anybody know any workaround or has any idea how to fix it? Thanks in advance!

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