C++11: Compile-time Array with Logarithmic Evaluation Depth

Question

One way to implement a C++11 array that has its elements initialized by a function of their index calculated by the compiler and have the results stored in the data section

Answer 1

If what you're using in the code is a weird form of the indices trick, here's an implementation that has O(log N) instantiations:

// using aliases for cleaner syntax
template using Invoke = typename T::type;

template struct seq{ using type = seq; };

template struct concat;

template
struct concat, seq>
  : seq{};

template
using Concat = Invoke>;

template struct gen_seq;
template using GenSeq = Invoke>;

template
struct gen_seq : Concat, GenSeq>{};

template<> struct gen_seq<0> : seq<>{};
template<> struct gen_seq<1> : seq<0>{};

// example

template
void f(seq);

int main(){
  f(gen_seq<6>());
}

Live example.