[FEATURE] Make strong type debug streamable.

include/seqan3/core/detail/strong_type.hpp

@@ -16,6 +16,7 @@
 #include <type_traits>
 
 #include <seqan3/core/add_enum_bitwise_operators.hpp>
+#include <seqan3/core/detail/debug_stream_type.hpp>
 #include <seqan3/core/type_traits/basic.hpp>
 
 namespace seqan3::detail
@@ -496,3 +497,35 @@ class strong_type
     //!\brief The underlying value, which is wrapped as a strong type.
     value_t value;
 };
+
+//------------------------------------------------------------------------------
+// related functions
+//------------------------------------------------------------------------------
+
+/*!\name Formatted output
+ * \relates seqan3::detail::strong_type
+ * \{
+ */
+
+/*!\brief Formatted output to a seqan3::detail::debug_stream_type.
+ * \tparam char_t The char type of the seqan3::detail::debug_stream_type.
+ * \tparam strong_type_t The strong type to print; must model seqan3::detail::strong_type_specialisation.
+ *
+ * \param[in,out] stream The output stream.
+ * \param[in] value The strong typed value to print.
+ *
+ * \details
+ *
+ * Prints the stored value of the given strong type.
+ *
+ * \returns `stream_t &` A reference to the given stream.
+ */
+template <typename char_t, strong_type_specialisation strong_type_t>
+debug_stream_type<char_t> & operator<<(debug_stream_type<char_t> & stream, strong_type_t && value)
+{
+    stream << value.get();
+    return stream;
+}
+//!\}
+
+} // namespace seqan3::detail

test/unit/core/detail/CMakeLists.txt

@@ -1,4 +1,5 @@
 seqan3_test(int_types_test.cpp)
 seqan3_test(pack_algorithm_test.cpp)
+seqan3_test(strong_type_debug_stream_test.cpp)
 seqan3_test(strong_type_test.cpp)
 seqan3_test(type_inspection_test.cpp)

test/unit/core/detail/strong_type_debug_stream_test.cpp

@@ -0,0 +1,25 @@
+// -----------------------------------------------------------------------------------------------------
+// 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/strong_type.hpp>
+
+struct my_type : seqan3::detail::strong_type<int, my_type>
+{
+    using seqan3::detail::strong_type<int, my_type>::strong_type;
+};
+
+TEST(strong_type, debug_stremable)
+{
+    my_type obj{10};
+
+    std::ostringstream buffer{};
+    seqan3::debug_stream_type stream{buffer};
+    stream << obj;
+    EXPECT_EQ(buffer.str(), "10");
+}