c 17 how to create a template instance with a non-type template-CodePudding

I want to create a body with a different part, and if I know the part's name, I can create the corresponding instance with a factory.Just as below:

template<typename Part>
class Body
{};

class Part1
{};

class Part2
{};

enum class E
{
    part1,
    part2,
};

template<E e>
class Factory
{
public:
    static unique_ptr<Body<>> create()
    {
        if (e == E::part1)
        {
            return make_unique<Body<Part1>>();
        }
        else
        {
            return make_unique<Body<Part2>>();
        }
    }   
};

int main()
{
    auto f=Factory<E::part1>();
    return 0;
}

Certainly it fails at compile time,so how could I get my porpuse?

CodePudding user response：

There's nothing here with a non-type template argument, so your title is confusing.

I assume your compiler error is complaining about

Body<>

Well, that's an error. Body is not a type, but a template. It needs an argument and there is no default.

The code wants it to be a Body<Part1> or a Body<Part2> but there is no such thing as a "Body of anything" as you implied.

You can have a type that holds either type by using a variant. For example,

using BodyPart = std::variant<Body<Part1>,Body<Part2>>;

But you'll have to learn how to use that value effectively (best with visitors), as it's not the same as a polymorphic type nor a generic (compile time) template.