From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Sat, 28 Aug 2021 22:23:37 +0000 (-0600)
Subject: Declare local difference_type for sparse matrix iterators.
X-Git-Tag: v9.4.0-rc1~1007^2~5
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e5eec705aa8c0b7d3020bf2d36a80f29d7e42c61;p=dealii.git

Declare local difference_type for sparse matrix iterators.
---

diff --git a/include/deal.II/lac/block_vector_base.h b/include/deal.II/lac/block_vector_base.h
index 015da300fa..87b5335127 100644
--- a/include/deal.II/lac/block_vector_base.h
+++ b/include/deal.II/lac/block_vector_base.h
@@ -141,9 +141,10 @@ namespace internal
                                   typename BlockVectorType::value_type>::type;
 
       /**
-       * Declare some alias which are standard for iterators and are used
+       * Declare some aliases that are standard for iterators and are used
        * by algorithms to enquire about the specifics of the iterators they
-       * work on.
+       * work on. (Example: `std::next()`, which needs to know about a local
+       * type named `difference_type`.)
        */
       using iterator_category = std::random_access_iterator_tag;
       using difference_type   = std::ptrdiff_t;
diff --git a/include/deal.II/lac/sparse_matrix.h b/include/deal.II/lac/sparse_matrix.h
index 8e9bab9078..ed2e4c4bce 100644
--- a/include/deal.II/lac/sparse_matrix.h
+++ b/include/deal.II/lac/sparse_matrix.h
@@ -360,6 +360,8 @@ namespace SparseMatrixIterators
      */
     using value_type = const Accessor<number, Constness> &;
 
+    using difference_type = size_type;
+
     /**
      * Constructor. Create an iterator into the matrix @p matrix for the given
      * index in the complete matrix (counting from the zeroth entry).