Populate an array of template pointers class via metaprogramming

Question

Basically I would like to have a static array of pointers to template classes. A sort of map from or lookup table where to an index corresponds a template class. II'll try to explain my question better with the code example below.

#include <iostream>

struct TemplateInterface
{
    virtual int get()  = 0;
};

template<int I>
struct TemplatedStruct : public TemplateInterface
{
    int get() override { return I; }
};

// --------------------------------------------------------------------------
// Refactor this section with metaprogramming so to have classes from 1 to N
// --------------------------------------------------------------------------
static TemplatedStruct<1> one;
static TemplatedStruct<2> two;
static TemplatedStruct<3> three;


static TemplateInterface* TIArray[3] = {&one, &two, &three};
// --------------------------------------------------------------------------


int main() {
    for(int i = 0; i < 3; ++i)
    {
        TemplateInterface* ptr = TIArray[i];
        std::cout << ptr->get() << std::endl;
    }
}

Are you sure you want them to be const? You are flirting with UB with that const_cast — AndyG
– AndyG, Commented Dec 31, 2020 at 14:31
@Jarod42 and [at]AndyG thanks, my mistake. I have updated the question to be more simple and clear. — giuseppe
– giuseppe, Commented Dec 31, 2020 at 14:36

Jarod42 · Accepted Answer · 2020-12-31 14:45:52Z

3

You might have

template <std::size_t... Is>
std::array<TemplateInterface*, sizeof...(Is)>
makeInterfaceArray(std::index_sequence<Is...>)
{
    static std::tuple<TemplatedStruct<Is>...> data{};
    return {{ &std::get<Is>(data)... }};
}

template <std::size_t N>
std::array<TemplateInterface*, N> makeInterfaceArray()
{
    return makeInterfaceArray(std::make_index_sequence<N>{});
}


int main() {
    for (TemplateInterface* ptr : makeInterfaceArray<3>())
    {
        std::cout << ptr->get() << std::endl;
    }
}

Demo

edited Dec 31, 2020 at 14:45

answered Dec 31, 2020 at 12:09

Jarod42

227k15 gold badges214 silver badges350 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

giuseppe Over a year ago

Thanks. Seems very clean, but I am not able to compile your code here godbolt.org/z/z618fs ... do I miss something?

Jarod42 Over a year ago

@giuseppe: Typo fixed, and Demo added.

Collectives™ on Stack Overflow

Populate an array of template pointers class via metaprogramming

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related