Why isn't a for-loop a compile-time expression?

Question

If I want to do something like iterate over a tuple, I have to resort to crazy template metaprogramming and template helper specializations. For example, the following progr

Answer 1

Here's a way to do it that does not need too much boilerplate, inspired from http://stackoverflow.com/a/26902803/1495627 :

template
struct num { static const constexpr auto value = N; };

template 
void for_(F func, std::index_sequence)
{
  using expander = int[];
  (void)expander{0, ((void)func(num{}), 0)...};
}

template 
void for_(F func)
{
  for_(func, std::make_index_sequence());
}

Then you can do :

for_([&] (auto i) {      
  std::get(t); // do stuff
});

If you have a C++17 compiler accessible, it can be simplified to

template 
void for_(F func, std::index_sequence)
{
  (func(num{}), ...);
}