null created by danieluranga - https://repl.it/HkrZ/10

HkrZ-10.cpp

#include <iostream>

enum Id
{
  A, B, C, D
};

struct Data
{
  Id id;
  const char* val;
};

constexpr Data arr[] =
{
  {A, "test"},
  {B, "otra cosa"},
  {C, "tercera"},
};

template<typename T, std::size_t size>
constexpr std::size_t GetArrLength(T(&)[size]) { return size; }

template<Id id>
class FindById
{
  private:
  
  template<Id id2, int index>
  struct FindById2
  {
    static constexpr const Data* value = (id == arr[index].id) ? &arr[index] : FindById2<id, index + 1>::value;
  };
  
  template<Id id2>
  struct FindById2<id2, GetArrLength(arr)>
  {
    static constexpr const Data* value = id == arr[GetArrLength(arr) - 1].id ? arr : nullptr;
  };
  
  public:
  
  static constexpr const Data* value = FindById2<id, 0>::value;
  static_assert(value != nullptr, "Value not found.");
};

int main()
{
  
  std::cout << "A: " << FindById<A>::value->val << std::endl;
  std::cout << "B: " << FindById<B>::value->val << std::endl;
  std::cout << "C: " << FindById<C>::value->val << std::endl;
}