language: C++11 (gcc-4.7.2)
date: 173 days 19 hours ago
link:
visibility: public 
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#include <type_traits>
 
template <typename T>
class smart_ptr
{
public:
    // ... removed other member functions for simplicity
    T* get() const { return ptr; }
 
private:
    template <typename... Args>
    struct opparen_constret
    {
        typedef decltype(std::declval<T const>()(std::declval<Args>()...)) type;
    };
 
    template <typename... Args>
    struct opparen_ret
    {
        typedef decltype(std::declval<T>()(std::declval<Args>()...)) type;
    };
 
public:
    template <typename... Args>
    typename opparen_constret<Args...>::type operator ()(Args... args) const
    {
        return (*get())(args...);
    }
 
    template <typename... Args>
    typename opparen_ret<Args...>::type operator ()(Args... args)
    {
        return (*get())(args...);
    }
 
private:
    T* ptr;
};
 
struct Test {};
 
int main()
{
    smart_ptr<Test> p;
    return 0;
}