In MITK Nightly mitkVector::ToArray(ArrayType array) function should pass the reference of the array:
In Modules\Core\include\mitkVector.h:
template <typename ArrayType > void ToArray(ArrayType& array) const
Also, the following test case should pass:
mitk::Vector3D vector_1; vector_1[0] = 4.6; vector_1[1] = 9.76543; vector_1[2] = 746.09; itk::Array<double> array_1(3); vector_1.ToArray(array_1); MITK_TEST_CONDITION(mitk::Equal(vector_1[0], array_1[0])); MITK_TEST_CONDITION(mitk::Equal(vector_1[1], array_1[1])); MITK_TEST_CONDITION(mitk::Equal(vector_1[2], array_1[2]));