num::square_extent_2d

Defined in header <core/index_space.hpp>

template <class G>
concept square_extent_2d = requires(const G &g) {
  { g.N } -> std::convertible_to<int>;
};

A square \(N \times N\) extent.

A structured grid and a periodic lattice share exactly this much structure: both are square and know their side length. Naming it makes the two families siblings rather than independent shapes that happen to spell N the same way.