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#include <string>
#include <map>
#include <iostream>
 
template <class T, class Factory> class add_ctor {
    public:
        template<Args...> add_ctor<Args&&...> : obj(Factory()(std::forward<Args>(args)...)) {}
    private:
        T* obj;
};
 
class A {
    public:
        std::string v;
        static A createOne();
    private:
        A();
};
A A::createOne() {
    A a;
    a.v = "Hello!";
    return a;
}
 
int main() {
    std::map<int, add_ctor<A, &A::createOne()> > as;
    std::cout << as[0].v << "\n";
    return 0;
}

prog.cpp:7:18: error: 'Args' has not been declared
prog.cpp:7:36: error: 'Args' was not declared in this scope
prog.cpp:7:42: error: expected parameter pack before '...'
prog.cpp:7:45: error: wrong number of template arguments (1, should be 2)
prog.cpp:5:41: error: provided for 'template<class T, class Factory> class add_ctor'
prog.cpp:7:47: error: expected unqualified-id before ':' token
prog.cpp: In function 'int main()':
prog.cpp:26:46: error: template argument 2 is invalid
prog.cpp:26:48: error: template argument 2 is invalid
prog.cpp:26:48: error: template argument 4 is invalid
prog.cpp:26:52: error: invalid type in declaration before ';' token
prog.cpp:27:22: error: invalid types 'int[int]' for array subscript

Standard output is empty