Editing Multiple dispatch (section)

==== D ====
{{As of|2021}}, as do many other object-oriented programming languages, [[D (programming language)|D]] natively supports only single dispatch. However, it is possible to emulate open multimethods as a library function in D. The ''openmethods'' library<ref name="openmethods">[https://github.com/jll63/methods.d openmethods], Open Multi-Methods for D by Jean-Louis Leroy.</ref> is an example.

<syntaxhighlight lang="d">
// Declaration
Matrix plus(virtual!Matrix, virtual!Matrix);

// The override for two DenseMatrix objects
@method
Matrix _plus(DenseMatrix a, DenseMatrix b)
{
  const int nr = a.rows;
  const int nc = a.cols;
  assert(a.nr == b.nr);
  assert(a.nc == b.nc);
  auto result = new DenseMatrix;
  result.nr = nr;
  result.nc = nc;
  result.elems.length = a.elems.length;
  result.elems[] = a.elems[] + b.elems[];
  return result;
}

// The override for two DiagonalMatrix objects
@method
Matrix _plus(DiagonalMatrix a, DiagonalMatrix b)
{
  assert(a.rows == b.rows);
  double[] sum;
  sum.length = a.elems.length;
  sum[] = a.elems[] + b.elems[];
  return new DiagonalMatrix(sum);
}
</syntaxhighlight>