Can a variable template be passed as a template template argument?

问题

The following nonsensical example does not compile, but is there some other way to pass a variable template as a template template argument?

template<typename T>
constexpr auto zero = T{0};

template<typename T, template<typename> auto VariableTemplate>
constexpr auto add_one()
{
    return VariableTemplate<T> + T{1};
}

int main()
{
    return add_one<int, zero>();
}

Try on Compiler Explorer

回答1:

Short answer: No.

Long answer: Yes you can using some indirection through a class template:

template<typename T>
constexpr auto zero = T{0};

template<typename T>
struct zero_global {
    static constexpr auto value = zero<T>;
};

template<typename T, template<typename> class VariableTemplate>
constexpr auto add_one()
{
    return VariableTemplate<T>::value + T{1};
}

int main()
{
    return add_one<int, zero_global>();
}

Live example

来源：https://stackoverflow.com/questions/58592312/can-a-variable-template-be-passed-as-a-template-template-argument