constexpr CalculateNumberOfOffsets() for ITK, C++ (clang)

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// To be discussed at https://discourse.itk.org/t/itk-neighborhoodrange-a-new-class-for-efficient-modern-c-style-iteration/833/54
// Tested compilers: clang 3.8.0 and MSVC 2017
// -- Niels Dekker, LKEB, Leiden University Medical Center, 2018

#include <array>

// Minimal version of itk::Size<VDimension>
template <unsigned int VDimension = 2>
struct Size
{
  std::size_t m_InternalArray[VDimension];
};

// Minimal version of proposed shape class from http://review.source.kitware.com/#/c/23389/
template <unsigned VImageDimension>
struct HyperrectangularImageNeighborhoodShape
{
  const Size<VImageDimension> m_Radius;

constexpr std::size_t CalculateNumberOfOffsets() const noexcept 
  {
    std::size_t result = 1;

for (const auto radiusValue: m_Radius.m_InternalArray)
    {
      result *= 2 * radiusValue + 1;
    }
    return result;
  }
};

int main()
{
  constexpr Size<> radius{ {3, 4} };
  constexpr HyperrectangularImageNeighborhoodShape<2> shape{ radius };
  constexpr std::size_t numberOfOffsets = shape.CalculateNumberOfOffsets();
  static_assert(numberOfOffsets == (2*3 + 1) * (2*4 + 1), "Yes!");

struct OffsetType {};
  std::array<OffsetType, numberOfOffsets> offsets{ {} };
}

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Compilation time: 0.67 sec, absolute running time: 0.31 sec, cpu time: 0.17 sec, memory peak: 3 Mb, absolute service time: 1,06 sec