Extracted min_category as a variadic metafunction.

The new min_category is similar to minimum_category but accepts variable
number of iterator categories on input instead of just two, and also does
not depend on Boost.MPL for lambda placeholders. The existing minimum_category
trait has been reimplemented in terms of min_category and deprecated.

We don't yet emit deprecation warnings as there is still code that uses
the old trait which we first need to update. Eventually, minimum_category
will emit warnings and will be removed.

test/Jamfile.v2

@@ -61,6 +61,9 @@ test-suite iterator
 
     [ run generator_iterator_test.cpp ]
 
+    [ run min_category.cpp ]
+    [ compile-fail min_category_compile_fail1.cpp ]
+    [ compile-fail min_category_compile_fail2.cpp ]
     [ run minimum_category.cpp ]
     [ compile-fail minimum_category_compile_fail.cpp ]
 

test/min_category.cpp

@@ -0,0 +1,33 @@
+// Copyright Andrey Semashev 2025.
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// https://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/iterator/min_category.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <iterator>
+#include <type_traits>
+
+using std::is_same;
+using boost::iterators::min_category;
+using boost::iterators::min_category_t;
+
+int main(int, char*[])
+{
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category<std::forward_iterator_tag>::type, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category<std::forward_iterator_tag, std::random_access_iterator_tag>::type, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category<std::random_access_iterator_tag, std::forward_iterator_tag>::type, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category<std::random_access_iterator_tag, std::random_access_iterator_tag>::type, std::random_access_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category<std::forward_iterator_tag, std::bidirectional_iterator_tag, std::random_access_iterator_tag>::type, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category<std::random_access_iterator_tag, std::bidirectional_iterator_tag, std::forward_iterator_tag>::type, std::forward_iterator_tag>));
+
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category_t<std::forward_iterator_tag>, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category_t<std::forward_iterator_tag, std::random_access_iterator_tag>, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category_t<std::random_access_iterator_tag, std::forward_iterator_tag>, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category_t<std::random_access_iterator_tag, std::random_access_iterator_tag>, std::random_access_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category_t<std::forward_iterator_tag, std::bidirectional_iterator_tag, std::random_access_iterator_tag>, std::forward_iterator_tag>));
+    BOOST_TEST_TRAIT_TRUE((is_same<min_category_t<std::random_access_iterator_tag, std::bidirectional_iterator_tag, std::forward_iterator_tag>, std::forward_iterator_tag>));
+
+    return boost::report_errors();
+}

test/min_category_compile_fail1.cpp

@@ -0,0 +1,19 @@
+// Copyright Andrey Semashev 2025.
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/iterator/min_category.hpp>
+
+using boost::iterators::min_category;
+
+struct A {};
+struct B {};
+
+int main(int, char*[])
+{
+    min_category<A, B>::type cat;
+
+    return 0;
+}

test/min_category_compile_fail2.cpp

@@ -0,0 +1,16 @@
+// Copyright Andrey Semashev 2025.
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/iterator/min_category.hpp>
+
+using boost::iterators::min_category;
+
+int main(int, char*[])
+{
+    min_category<>::type cat;
+
+    return 0;
+}

test/test_cmake/main.cpp

@@ -26,6 +26,7 @@
 #include <boost/iterator/iterator_concepts.hpp>
 #include <boost/iterator/iterator_facade.hpp>
 #include <boost/iterator/iterator_traits.hpp>
+#include <boost/iterator/min_category.hpp>
 #include <boost/iterator/minimum_category.hpp>
 #include <boost/iterator/new_iterator_tests.hpp>
 #include <boost/iterator/permutation_iterator.hpp>