Is it possible to develop static for loop in c++?

Question

Is it possible for something like this to exist?

template
void deduce_mask(Matrix const &src, int mask[])
{
    //I hope i could b         


        

Answer 1

lego's response, while elegant and awesome, won't compile if you want the index to go into a template - e.g. std::get(some_tuple)

In case you want to implement this additional feature in the future, the below code will work and should be backwards-compatible with lego's solution (except that I use a static apply method instead of operator()):

template 
struct static_for
{
    template 
    static inline constexpr void apply(Lambda const& f)
    {
        if (First < Last)
        {
            f(std::integral_constant{});
            static_for::apply(f);
        }
    }
};
template 
struct static_for
{
    template 
    static inline constexpr void apply(Lambda const& f) {}
};

Now you can do the following:

static_for<0, Channel>::apply([&](auto i) // Changed from '(int i)'. In general, 'auto' will be a better choice for metaprogramming!
{            
    // code...
    mask[mapper(0, 1, i)] = src(row - 1, col)[i]; // Notice that this does not change
    std::get(some_tuple); // But here you must get the member .value
    // more code...
});

Tested in VC++ 2015. I didn't research why this works, but I can only assume that std::integral_constant defines an implicit cast to T using value, but the compiler can't figure out that the implicit cast produces a constexpr, so you have to retrieve the value using i.value, which is a constexpr.

Addressing @tom's question in the comment If you want to iterate over a parameter pack, you can do the following (same implementation):

template
inline constexpr auto foo(const Args&... args)
{
    static_for<0,sizeof...(Args)>::apply([&](auto N)
    {
        std::cout << std::get(std::make_tuple(args...));
    });
}

foo(1,"a",2.5); // This does exactly what you think it would do

If std::get(std::make_tuple(args...)) looks ugly, you can create another constexpr function that minimizes the code.