introduce new seqan3::detail::transfer_type_modifier_onto (#2365)

* [FEATURE] introduce new seqan3::detail::transfer_type_modifier_onto

* [FEATURE] use new seqan3::detail::transfer_type_modifier_onto

* Update include/seqan3/core/detail/transfer_type_modifier_onto.hpp

Co-authored-by: Jörg Winkler <[email protected]>

* Update include/seqan3/core/detail/transfer_type_modifier_onto.hpp

* Update include/seqan3/core/detail/transfer_type_modifier_onto.hpp

Co-authored-by: Enrico Seiler <[email protected]>

* Update include/seqan3/core/detail/transfer_type_modifier_onto.hpp

Co-authored-by: Enrico Seiler <[email protected]>

Co-authored-by: Jörg Winkler <[email protected]>
Co-authored-by: Enrico Seiler <[email protected]>

include/seqan3/core/configuration/configuration.hpp

@@ -17,6 +17,7 @@
 #include <seqan3/core/algorithm/pipeable_config_element.hpp>
 #include <seqan3/core/configuration/detail/concept.hpp>
 #include <seqan3/core/configuration/detail/configuration_utility.hpp>
+#include <seqan3/core/detail/transfer_type_modifier_onto.hpp>
 #include <seqan3/utility/tuple_utility.hpp>
 #include <seqan3/utility/type_list/type_list.hpp>
 #include <seqan3/utility/type_pack/traits.hpp>
@@ -201,15 +202,10 @@ class configuration : public std::tuple<configs_t...>
 
             // Get the actual base tuple type from the other configuration.
             using other_base_t = typename std::remove_cvref_t<other_configuration_t>::base_type;
-            // The other base tuple type matching the const qualifier of the input parameter.
-            using other_base_maybe_const_t =
-                std::conditional_t<std::is_const_v<std::remove_reference_t<other_configuration_t>>,
-                                   std::add_const_t<other_base_t>,
-                                   other_base_t>;
+
             // The other base tuple type matching the reference type and the const qualifier of the input parameter.
-            using fwd_other_base_t = std::conditional_t<std::is_lvalue_reference_v<other_configuration_t>,
-                                                        std::add_lvalue_reference_t<other_base_maybe_const_t>,
-                                                        std::add_rvalue_reference_t<other_base_maybe_const_t>>;
+            using other_base_same_modifier_t = detail::transfer_type_modifier_onto_t<other_configuration_t,
+                                                                                     other_base_t>;
 
             // Form a new seqan3::configuration type with the concatenated configuration element types of this and the
             // other configuration.
@@ -221,7 +217,7 @@ class configuration : public std::tuple<configs_t...>
 
             // Concatenate the two configurations using their base tuple types.
             return appended_configuration_t{std::tuple_cat(static_cast<base_type>(*this),
-                                                           static_cast<fwd_other_base_t>(other_config))};
+                                                           std::forward<other_base_same_modifier_t>(other_config))};
         }
     }
 

include/seqan3/core/detail/transfer_type_modifier_onto.hpp

@@ -0,0 +1,70 @@
+// -----------------------------------------------------------------------------------------------------
+// Copyright (c) 2006-2020, Knut Reinert & Freie Universität Berlin
+// Copyright (c) 2016-2020, Knut Reinert & MPI für molekulare Genetik
+// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
+// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
+// -----------------------------------------------------------------------------------------------------
+
+/*!\file
+ * \author Marcel Ehrhardt <marcel.ehrhardt AT fu-berlin.de>
+ * \brief Provides type traits seqan3::detail::transfer_type_modifier_onto.
+ */
+
+#pragma once
+
+#include <seqan3/std/type_traits>
+
+#include <seqan3/core/platform.hpp>
+
+namespace seqan3::detail
+{
+
+/*!\brief Transfers the type modifier `&`, `&&` and `const` (and any combination) to the target type.
+ * \implements seqan3::transformation_trait
+ * \tparam source_t The type you wish to transfer the type modifier from.
+ * \tparam target_t The type you wish to transfer the type modifier to.
+ * \ingroup core
+ * If the `target_t` already has a type modifier, e.g. `const`, it will keep that type modifier.
+ *
+ * If the resulting type would have the type modifier `&&` and `&` at the same time, it follows the rule of reference
+ * collapsing, that means `&` will be preferred.
+ * \sa https://en.cppreference.com/w/cpp/language/reference#Reference_collapsing
+ */
+template <typename source_t, typename target_t>
+struct transfer_type_modifier_onto
+{
+private:
+    //!\brief Transfers the `const` type modifier to the target type.
+    using maybe_const_target_t = std::conditional_t<std::is_const_v<std::remove_reference_t<source_t>> ||
+                                                    std::is_const_v<std::remove_reference_t<target_t>>,
+                                                    std::add_const_t<std::remove_cvref_t<target_t>>,
+                                                    std::remove_cvref_t<target_t>>;
+
+    //!\brief Transfers the `&&` type modifier to the target type.
+    using maybe_rvalue_reference_t = std::conditional_t<std::is_rvalue_reference_v<source_t> ||
+                                                        std::is_rvalue_reference_v<target_t>,
+                                                        std::add_rvalue_reference_t<maybe_const_target_t>,
+                                                        maybe_const_target_t>;
+
+    //!\brief Transfers the `&` type modifier to the target type.
+    using maybe_lvalue_reference_target_t = std::conditional_t<std::is_lvalue_reference_v<source_t> ||
+                                                               std::is_lvalue_reference_v<target_t>,
+                                                               std::add_lvalue_reference_t<maybe_rvalue_reference_t>,
+                                                               maybe_rvalue_reference_t>;
+public:
+
+    //!\brief Transfers the type modifier `&`, `&&` and `const` (and any combination) to the target type.
+    using type = maybe_lvalue_reference_target_t;
+};
+
+/*!\brief Transfers the type modifier `&`, `&&` and `const` (and any combination) to the target type
+ *        (transformation_trait shortcut).
+ * \tparam source_t The type you wish to transfer the type modifier from.
+ * \tparam target_t The type you wish to transfer the type modifier to.
+ * \see seqan3::detail::transfer_type_modifier_onto
+ * \relates seqan3::detail::transfer_type_modifier_onto
+ */
+template <typename source_t, typename target_t>
+using transfer_type_modifier_onto_t = typename transfer_type_modifier_onto<source_t, target_t>::type;
+
+} // namespace seqan3::detail

test/unit/core/detail/CMakeLists.txt

@@ -6,4 +6,5 @@ seqan3_test(pack_algorithm_test.cpp)
 seqan3_test(strong_type_debug_stream_test.cpp)
 seqan3_test(strong_type_test.cpp)
 seqan3_test(template_inspection_test.cpp)
+seqan3_test(transfer_type_modifier_onto_test.cpp)
 seqan3_test(type_name_as_string_test.cpp)

test/unit/core/detail/transfer_type_modifier_onto_test.cpp

@@ -0,0 +1,142 @@
+// -----------------------------------------------------------------------------------------------------
+// Copyright (c) 2006-2020, Knut Reinert & Freie Universität Berlin
+// Copyright (c) 2016-2020, Knut Reinert & MPI für molekulare Genetik
+// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
+// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
+// -----------------------------------------------------------------------------------------------------
+
+#include <gtest/gtest.h>
+
+#include <seqan3/core/detail/transfer_type_modifier_onto.hpp>
+#include <seqan3/test/expect_same_type.hpp>
+
+TEST(transfer_type_modifier_onto, type)
+{
+    // target type has no modifier
+    EXPECT_SAME_TYPE(double, (typename seqan3::detail::transfer_type_modifier_onto<int, double>::type));
+    EXPECT_SAME_TYPE(double &, (typename seqan3::detail::transfer_type_modifier_onto<int &, double>::type));
+    EXPECT_SAME_TYPE(double &&, (typename seqan3::detail::transfer_type_modifier_onto<int &&, double>::type));
+    EXPECT_SAME_TYPE(double const, (typename seqan3::detail::transfer_type_modifier_onto<int const, double>::type));
+    EXPECT_SAME_TYPE(double const &, (typename seqan3::detail::transfer_type_modifier_onto<int const &, double>::type));
+    EXPECT_SAME_TYPE(double const &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &&, double>::type));
+
+    // target type has lvalue reference modifier
+    EXPECT_SAME_TYPE(double &, (typename seqan3::detail::transfer_type_modifier_onto<int, double &>::type));
+    EXPECT_SAME_TYPE(double & /*&*/, (typename seqan3::detail::transfer_type_modifier_onto<int &, double &>::type));
+    EXPECT_SAME_TYPE(double & /*&&*/, (typename seqan3::detail::transfer_type_modifier_onto<int &&, double &>::type));
+    EXPECT_SAME_TYPE(double const &, (typename seqan3::detail::transfer_type_modifier_onto<int const, double &>::type));
+    EXPECT_SAME_TYPE(double const & /*&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &, double &>::type));
+    EXPECT_SAME_TYPE(double const & /*&&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &&, double &>::type));
+
+    // target type has rvalue reference modifier
+    EXPECT_SAME_TYPE(double &&, (typename seqan3::detail::transfer_type_modifier_onto<int, double &&>::type));
+    EXPECT_SAME_TYPE(double /*&&*/ &, (typename seqan3::detail::transfer_type_modifier_onto<int &, double &&>::type));
+    EXPECT_SAME_TYPE(double && /*&&*/, (typename seqan3::detail::transfer_type_modifier_onto<int &&, double &&>::type));
+    EXPECT_SAME_TYPE(double const &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const, double &&>::type));
+    EXPECT_SAME_TYPE(double const /*&&*/ &,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &, double &&>::type));
+    EXPECT_SAME_TYPE(double const /*&&*/ &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &&, double &&>::type));
+
+    // target type has const modifier
+    EXPECT_SAME_TYPE(double const, (typename seqan3::detail::transfer_type_modifier_onto<int, double const>::type));
+    EXPECT_SAME_TYPE(double const &, (typename seqan3::detail::transfer_type_modifier_onto<int &, double const>::type));
+    EXPECT_SAME_TYPE(double const &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int &&, double const>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const, double const>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const &,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &, double const>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &&, double const>::type));
+
+    // target type has const lvalue reference modifier
+    EXPECT_SAME_TYPE(double const &, (typename seqan3::detail::transfer_type_modifier_onto<int, double const &>::type));
+    EXPECT_SAME_TYPE(double const & /*&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int &, double const &>::type));
+    EXPECT_SAME_TYPE(double const & /*&&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int &&, double const &>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const &,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const, double const &>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const & /*&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &, double const &>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const & /*&&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &&, double const &>::type));
+
+    // target type has const rvalue reference modifier
+    EXPECT_SAME_TYPE(double const &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int, double const &&>::type));
+    EXPECT_SAME_TYPE(double const /*&&*/ &,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int &, double const &&>::type));
+    EXPECT_SAME_TYPE(double const && /*&&*/,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int &&, double const &&>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const, double const &&>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const /*&&*/ &,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &, double const &&>::type));
+    EXPECT_SAME_TYPE(double /*const*/ const /*&&*/ &&,
+                     (typename seqan3::detail::transfer_type_modifier_onto<int const &&, double const &&>::type));
+}
+
+TEST(transfer_type_modifier_onto, type_t_helper)
+{
+    // target type has no modifier
+    EXPECT_SAME_TYPE(double, (seqan3::detail::transfer_type_modifier_onto_t<int, double>));
+    EXPECT_SAME_TYPE(double &, (seqan3::detail::transfer_type_modifier_onto_t<int &, double>));
+    EXPECT_SAME_TYPE(double &&, (seqan3::detail::transfer_type_modifier_onto_t<int &&, double>));
+    EXPECT_SAME_TYPE(double const, (seqan3::detail::transfer_type_modifier_onto_t<int const, double>));
+    EXPECT_SAME_TYPE(double const &, (seqan3::detail::transfer_type_modifier_onto_t<int const &, double>));
+    EXPECT_SAME_TYPE(double const &&, (seqan3::detail::transfer_type_modifier_onto_t<int const &&, double>));
+
+    // target type has lvalue reference modifier
+    EXPECT_SAME_TYPE(double &, (seqan3::detail::transfer_type_modifier_onto_t<int, double &>));
+    EXPECT_SAME_TYPE(double & /*&*/, (seqan3::detail::transfer_type_modifier_onto_t<int &, double &>));
+    EXPECT_SAME_TYPE(double & /*&&*/, (seqan3::detail::transfer_type_modifier_onto_t<int &&, double &>));
+    EXPECT_SAME_TYPE(double const &, (seqan3::detail::transfer_type_modifier_onto_t<int const, double &>));
+    EXPECT_SAME_TYPE(double const & /*&*/, (seqan3::detail::transfer_type_modifier_onto_t<int const &, double &>));
+    EXPECT_SAME_TYPE(double const & /*&&*/, (seqan3::detail::transfer_type_modifier_onto_t<int const &&, double &>));
+
+    // target type has rvalue reference modifier
+    EXPECT_SAME_TYPE(double &&, (seqan3::detail::transfer_type_modifier_onto_t<int, double &&>));
+    EXPECT_SAME_TYPE(double /*&&*/ &, (seqan3::detail::transfer_type_modifier_onto_t<int &, double &&>));
+    EXPECT_SAME_TYPE(double && /*&&*/, (seqan3::detail::transfer_type_modifier_onto_t<int &&, double &&>));
+    EXPECT_SAME_TYPE(double const &&, (seqan3::detail::transfer_type_modifier_onto_t<int const, double &&>));
+    EXPECT_SAME_TYPE(double const /*&&*/ &, (seqan3::detail::transfer_type_modifier_onto_t<int const &, double &&>));
+    EXPECT_SAME_TYPE(double const /*&&*/ &&, (seqan3::detail::transfer_type_modifier_onto_t<int const &&, double &&>));
+
+    // target type has const modifier
+    EXPECT_SAME_TYPE(double const, (seqan3::detail::transfer_type_modifier_onto_t<int, double const>));
+    EXPECT_SAME_TYPE(double const &, (seqan3::detail::transfer_type_modifier_onto_t<int &, double const>));
+    EXPECT_SAME_TYPE(double const &&, (seqan3::detail::transfer_type_modifier_onto_t<int &&, double const>));
+    EXPECT_SAME_TYPE(double /*const*/ const, (seqan3::detail::transfer_type_modifier_onto_t<int const, double const>));
+    EXPECT_SAME_TYPE(double /*const*/ const &,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const &, double const>));
+    EXPECT_SAME_TYPE(double /*const*/ const &&,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const &&, double const>));
+
+    // target type has const lvalue reference modifier
+    EXPECT_SAME_TYPE(double const &, (seqan3::detail::transfer_type_modifier_onto_t<int, double const &>));
+    EXPECT_SAME_TYPE(double const & /*&*/, (seqan3::detail::transfer_type_modifier_onto_t<int &, double const &>));
+    EXPECT_SAME_TYPE(double const & /*&&*/, (seqan3::detail::transfer_type_modifier_onto_t<int &&, double const &>));
+    EXPECT_SAME_TYPE(double /*const*/ const &,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const, double const &>));
+    EXPECT_SAME_TYPE(double /*const*/ const & /*&*/,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const &, double const &>));
+    EXPECT_SAME_TYPE(double /*const*/ const & /*&&*/,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const &&, double const &>));
+
+    // target type has const rvalue reference modifier
+    EXPECT_SAME_TYPE(double const &&, (seqan3::detail::transfer_type_modifier_onto_t<int, double const &&>));
+    EXPECT_SAME_TYPE(double const /*&&*/ &, (seqan3::detail::transfer_type_modifier_onto_t<int &, double const &&>));
+    EXPECT_SAME_TYPE(double const && /*&&*/, (seqan3::detail::transfer_type_modifier_onto_t<int &&, double const &&>));
+    EXPECT_SAME_TYPE(double /*const*/ const &&,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const, double const &&>));
+    EXPECT_SAME_TYPE(double /*const*/ const /*&&*/ &,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const &, double const &&>));
+    EXPECT_SAME_TYPE(double /*const*/ const /*&&*/ &&,
+                     (seqan3::detail::transfer_type_modifier_onto_t<int const &&, double const &&>));
+}