In c++ 11, how to invoke an arbitrary callable object?

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Rather than implementing INVOKE yourself, use one of the library features that uses it. In particular, std::reference_wrapper works. Thus you can have the effect of std::invoke(f, args...) with std::ref(f)(args...):

template<typename F, typename... Args>
auto invoke(F f, Args&&... args)
    -> decltype(std::ref(f)(std::forward<Args>(args)...))
{
    return std::ref(f)(std::forward<Args>(args)...);
}

I didn’t forward f because std::reference_wrapper requires that the object passed in is not an rvalue. Using std::bind instead of std::ref doesn’t fix the problem. What this means is that for a function object like this:

struct F
{
    void operator()() && {
        std::cout << "Rvalue\n";
    }
    void operator()() const& {
        std::cout << "Lvalue\n";
    }
};

invoke(F{}) will print Lvalue, whereas std::invoke(F{}) in C++17 would print Rvalue.

I found the technique from this paper

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