How can I curry variadic template template parameters?

Question

Variadic template template parameters accept any template:

template
struct Test1 {
    using type = int;
};

template

        

Answer 1

Simple solution is:

template
    <
        template  class BeCurry,
        typename... Params
    >
struct Currying
{
    template 
    using curried = BeCurry;

    template 
    using type = typename curried::type;

    template 
    using apply = Currying;
};

But it does not work with templates like Test1 and Test2 due to compilation errors (under gcc, at least). A workaround for this problem looks like this:

template
    <
        template  class BeCurry,
        typename... Params
    >
struct Curry
{
    using type = BeCurry;
};

template
    <
        template  class BeCurry
    >
struct Curry
{
    using type = BeCurry<>;
};

And now lines

template 
using curried = BeCurry;

should be replaced with lines

template 
using curried = typename Curry::type;

Example of using:

#include 
#include 

template 
void print_type(T t)
{
    std::cout << typeid(t).name() << std::endl;
}

// ...

print_type(Currying::type{});
print_type(Currying::apply::type<>{});
print_type(Currying::type{});
print_type(Currying::apply::type{});
print_type(Currying::apply::apply::type<>{});
print_type(Currying::apply::type<>{});

Full example at ideone.