Merge pull request #67 from h-2/doxygen196

[fix] minor optimisation

Author: h-2

include/bio/ranges/views/char_to.hpp

@@ -354,20 +354,27 @@ class char_to_cigar_view<urng_t>::iterator
     //!\brief Dereference operator returns element currently pointed at.
     constexpr value_type operator*() const
     {
-        alphabet::cigar c;
-
-        if constexpr (std::contiguous_iterator<uit_t>)
+        if (value == default_value)
         {
-            std::string_view v{uit_left, uit_right};
-            c.assign_string(v);
+            alphabet::cigar c;
+
+            if constexpr (std::contiguous_iterator<uit_t>)
+            {
+                std::string_view v{uit_left, uit_right};
+                c.assign_string(v);
+            }
+            else
+            {
+                std::string s;
+                std::ranges::copy(uit_left, uit_right, std::back_inserter(s));
+                c.assign_string(s);
+            }
+            return c;
         }
         else
         {
-            std::string s;
-            std::ranges::copy(uit_left, uit_right, std::back_inserter(s));
-            c.assign_string(s);
+            return value;
         }
-        return c;
     }
 
     //!\brief Return pointer to this iterator.

test/unit/ranges/views/view_char_to_test.cpp

@@ -195,8 +195,14 @@ TEST(view_char_to_cigar, typical_const)
     EXPECT_FALSE((std::ranges::output_range<decltype(v), bio::alphabet::cigar>));
     EXPECT_FALSE((std::ranges::output_range<decltype(v), char>));
 
-    auto const it = v.begin();
-    EXPECT_EQ(*it, (bio::alphabet::cigar{42, 'I'_cigar_op}));
+    auto it = v.begin();
+    EXPECT_EQ(*it, (bio::alphabet::cigar{42, 'I'_cigar_op}));                // updates the cache
+    EXPECT_EQ(*it, (bio::alphabet::cigar{42, 'I'_cigar_op}));                // uses the cache
+    EXPECT_EQ(*std::as_const(it), (bio::alphabet::cigar{42, 'I'_cigar_op})); // uses the cache
+
+    auto const it2 = v.begin();
+    EXPECT_EQ(*it2, (bio::alphabet::cigar{42, 'I'_cigar_op})); // does not update cache, because const
+    EXPECT_EQ(*it2, (bio::alphabet::cigar{42, 'I'_cigar_op})); // does not use cache, because it wasn't set
 }
 
 TEST(view_char_to_cigar, empty)