Change Tensor::unroll() to take iterator pairs.

include/deal.II/base/tensor.h

@@ -365,6 +365,17 @@ class Tensor<0, dim, Number>
   constexpr DEAL_II_CUDA_HOST_DEV real_type
   norm_square() const;
 
+  /**
+   * Fill a range with all tensor elements. Since this type of Tensor only has
+   * one entry this just copies the value of this tenso into <tt>*begin</tt>.
+   *
+   * The template type Number must be convertible to the type of
+   * <tt>*begin</tt>.
+   */
+  template <class Iterator>
+  void
+  unroll(const Iterator begin, const Iterator end) const;
+
   /**
    * Read or write the data of this object to or from a stream for the purpose
    * of serialization using the [BOOST serialization
@@ -774,11 +785,28 @@ class Tensor
    * This function unrolls all tensor entries into a single, linearly numbered
    * vector. As usual in C++, the rightmost index of the tensor marches
    * fastest.
+   *
+   * @deprecated Use the more general function that takes a pair of iterators
+   * instead.
    */
   template <typename OtherNumber>
-  void
+  DEAL_II_DEPRECATED_EARLY void
   unroll(Vector<OtherNumber> &result) const;
 
+  /**
+   * Fill a range with all tensor elements.
+   *
+   * This function unrolls all tensor entries into a single, linearly numbered
+   * sequence. As usual in C++, the rightmost index of the tensor marches
+   * fastest.
+   *
+   * The template type Number must be convertible to the type of
+   * <tt>*begin</tt>.
+   */
+  template <class Iterator>
+  void
+  unroll(const Iterator begin, const Iterator end) const;
+
   /**
    * Return an unrolled index in the range $[0,\text{dim}^{\text{rank}}-1]$
    * for the element of the tensor indexed by the argument to the function.
@@ -1029,6 +1057,7 @@ constexpr inline DEAL_II_ALWAYS_INLINE
 }
 
 
+
 template <int dim, typename Number>
 template <typename OtherNumber>
 constexpr inline DEAL_II_ALWAYS_INLINE
@@ -1201,6 +1230,7 @@ constexpr DEAL_II_CUDA_HOST_DEV inline DEAL_II_ALWAYS_INLINE
 }
 
 
+
 template <int dim, typename Number>
 template <typename Iterator>
 Iterator
@@ -1215,6 +1245,7 @@ Tensor<0, dim, Number>::unroll_recursion(const Iterator current,
 }
 
 
+
 template <int dim, typename Number>
 constexpr inline void
 Tensor<0, dim, Number>::clear()
@@ -1225,6 +1256,18 @@ Tensor<0, dim, Number>::clear()
 }
 
 
+
+template <int dim, typename Number>
+template <class Iterator>
+inline void
+Tensor<0, dim, Number>::unroll(const Iterator begin, const Iterator end) const
+{
+  AssertDimension(std::distance(begin, end), n_independent_components);
+  unroll_recursion(begin, end);
+}
+
+
+
 template <int dim, typename Number>
 template <class Archive>
 inline void
@@ -1694,18 +1737,29 @@ constexpr inline DEAL_II_ALWAYS_INLINE DEAL_II_CUDA_HOST_DEV
 }
 
 
+
 template <int rank_, int dim, typename Number>
 template <typename OtherNumber>
 inline void
 Tensor<rank_, dim, Number>::unroll(Vector<OtherNumber> &result) const
 {
-  AssertDimension(result.size(),
-                  (Utilities::fixed_power<rank_, unsigned int>(dim)));
+  unroll(result.begin(), result.end());
+}
+
+
 
-  unroll_recursion(result.begin(), result.end());
+template <int rank_, int dim, typename Number>
+template <class Iterator>
+inline void
+Tensor<rank_, dim, Number>::unroll(const Iterator begin,
+                                   const Iterator end) const
+{
+  AssertDimension(std::distance(begin, end), n_independent_components);
+  unroll_recursion(begin, end);
 }
 
 
+
 template <int rank_, int dim, typename Number>
 template <typename Iterator>
 Iterator