#include <iostream>

void func()
{
    std::cout << "Hello";
}

auto t = []{ func(); };
typedef decltype(t) functor_type;

template <class F>
void functor_caller()
{
    F f;
    f();
}

int main()
{
    functor_caller<functor_type>();
    return 0;
}

error: use of deleted function  '<lambda()>::<lambda>()'

error: a lambda closure type has a deleted default constructor

#define WRAP_FUNC(f)
struct f##_functor
{
    template <class... Args >
    auto operator()(Args ... args) ->decltype(f(args...))
    {
        return f(args...);
    }
};

WRAP_FUNC(func);

functor_caller<func_functor>()

{
    int n = 0;
    auto t = [&n](int a) -> int { return n += a; };
}

std::function<int(int)> F = t;

template <typename F>
int compute(int a, int b, F f)
{
    return a * f(b);  // example
}

template<class F>
struct wrapper
{
    static_assert(std::is_empty<F>(), "Lambdas must be empty");
    template<class... Ts>
    auto operator()(Ts&&... xs) const -> decltype(reinterpret_cast<const F&>(*this)(std::forward<Ts>(xs)...))
    {
        return reinterpret_cast<const F&>(*this)(std::forward<Ts>(xs)...);
    }
};

template <class F>
void function_caller()
{
    wrapper<F> f;
    f();
}