Math: fix a build issue with CUDA on Windows.

doc/changelog.dox

@@ -369,6 +369,9 @@ See also:
 -   Removed mention of the outdated Ubuntu PPA from @ref building as it doesn't
     seem to be maintained anymore (see
     [mosra/magnum-examples#61](https://github.com/mosra/magnum-examples/issues/61))
+-   Worked around a bug in the NVCC compiler on Windows involving
+    @ref Math::RectangularMatrix::DiagonalSize to make Magnum usable with CUDA
+    (see [mosra/magnum#345](https://github.com/mosra/magnum/issues/345))
 
 @subsection changelog-latest-bugfixes Bug fixes
 

src/Magnum/Math/RectangularMatrix.h

@@ -407,7 +407,12 @@ template<std::size_t cols, std::size_t rows, class T> class RectangularMatrix {
          *
          * @see @ref fromDiagonal()
          */
-        constexpr Vector<DiagonalSize, T> diagonal() const;
+        constexpr Vector<DiagonalSize, T> diagonal() const {
+            /* NVCC (from CUDA) has problems compiling this function under
+               Windows when there's a separate definition due to DiagonalSize
+               (see https://github.com/mosra/magnum/issues/345 for details) */
+            return diagonalInternal(typename Implementation::GenerateSequence<DiagonalSize>::Type());
+        }
 
         /**
          * @brief Convert matrix to vector
@@ -754,8 +759,6 @@ template<std::size_t cols, std::size_t rows, class T> inline RectangularMatrix<r
     return out;
 }
 
-template<std::size_t cols, std::size_t rows, class T> constexpr auto RectangularMatrix<cols, rows, T>::diagonal() const -> Vector<DiagonalSize, T> { return diagonalInternal(typename Implementation::GenerateSequence<DiagonalSize>::Type()); }
-
 #ifndef DOXYGEN_GENERATING_OUTPUT
 template<std::size_t cols, std::size_t rows, class T> template<std::size_t ...sequence> constexpr auto RectangularMatrix<cols, rows, T>::diagonalInternal(Implementation::Sequence<sequence...>) const -> Vector<DiagonalSize, T> {
     return {_data[sequence][sequence]...};