Add range + iterator overload for timmerge

Range overload supports temporaries.
Also change a missed std::less<> into std::ranges::less.

Author: Morwenn

README.md

@@ -55,6 +55,15 @@ template <
     requires std::sortable<Iterator, Compare, Projection>
 void timmerge(Iterator first, Iterator middle, Iterator last,
               Compare compare={}, Projection projection={});
+
+template <
+    std::ranges::random_access_range Range,
+    typename Compare = std::ranges::less,
+    typename Projection = std::identity
+>
+    requires std::sortable<std::ranges::iterator_t<Range>, Compare, Projection>
+void timmerge(Range &&range, std::ranges::iterator_t<Range> middle,
+              Compare compare={}, Projection projection={})
 ```
 
 ## EXAMPLE

include/gfx/timsort.hpp

@@ -695,7 +695,7 @@ template <typename RandomAccessIterator, typename Compare, typename Projection>
  */
 template <
     std::random_access_iterator Iterator,
-    typename Compare = std::less<>,
+    typename Compare = std::ranges::less,
     typename Projection = std::identity
 >
     requires std::sortable<Iterator, Compare, Projection>
@@ -707,6 +707,22 @@ void timmerge(Iterator first, Iterator middle, Iterator last,
     GFX_TIMSORT_AUDIT(std::is_sorted(first, last, comp, proj) && "Postcondition");
 }
 
+/**
+ * Stably merges two sorted halves [first, middle) and [middle, last) of a range into one
+ * sorted range [first, last) with a comparison function and a projection function.
+ */
+template <
+    std::ranges::random_access_range Range,
+    typename Compare = std::ranges::less,
+    typename Projection = std::identity
+>
+    requires std::sortable<std::ranges::iterator_t<Range>, Compare, Projection>
+void timmerge(Range &&range, std::ranges::iterator_t<Range> middle,
+              Compare comp={}, Projection proj={})
+{
+    gfx::timmerge(std::begin(range), middle, std::end(range), comp, proj);
+}
+
 /**
  * Stably sorts a range with a comparison function and a projection function.
  */

tests/cxx_20_tests.cpp

@@ -12,6 +12,20 @@
 #include "test_helpers.hpp"
 
 TEST_CASE( "support for temporary types" ) {
+    SECTION( "timsmerge over std::span" ) {
+        std::vector<int> vec(100);
+        std::iota(vec.begin(), vec.end(), -25);
+        test_helpers::shuffle(vec);
+
+        auto middle = vec.begin() + 38;
+        gfx::timsort(vec.begin(), middle);
+        gfx::timsort(middle, vec.end());
+
+        auto view = std::span(vec);
+        gfx::timmerge(std::span(vec), view.begin() + 38);
+        CHECK(std::ranges::is_sorted(vec));
+    }
+
     SECTION( "timsort over std::span" ) {
         std::vector<int> vec(50);
         std::iota(vec.begin(), vec.end(), -25);