Use std::data and std::size for boost equivalents, when possible

include/boost/core/data.hpp

@@ -8,8 +8,20 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_CORE_DATA_HPP
 #define BOOST_CORE_DATA_HPP
 
-#include <initializer_list>
+#include <iterator>
+
+// Note: MSVC doesn't define __cpp_lib_nonmember_container_access but supports the feature even in C++14 mode
+#if (defined(__cpp_lib_nonmember_container_access) && (__cpp_lib_nonmember_container_access >= 201411l)) || \
+    (defined(_MSC_VER) && (_MSC_VER >= 1900))
+
+namespace boost {
+using std::data;
+} /* boost */
+
+#else // (defined(__cpp_lib_nonmember_container_access) ...
+
 #include <cstddef>
+#include <initializer_list>
 
 namespace boost {
 
@@ -43,4 +55,6 @@ data(std::initializer_list<T> l) noexcept
 
 } /* boost */
 
+#endif // (defined(__cpp_lib_nonmember_container_access) ...
+
 #endif

include/boost/core/size.hpp

@@ -8,6 +8,18 @@ Distributed under the Boost Software License, Version 1.0.
 #ifndef BOOST_CORE_SIZE_HPP
 #define BOOST_CORE_SIZE_HPP
 
+#include <iterator>
+
+// Note: MSVC doesn't define __cpp_lib_nonmember_container_access but supports the feature even in C++14 mode
+#if (defined(__cpp_lib_nonmember_container_access) && (__cpp_lib_nonmember_container_access >= 201411l)) || \
+    (defined(_MSC_VER) && (_MSC_VER >= 1900))
+
+namespace boost {
+using std::size;
+} /* boost */
+
+#else // (defined(__cpp_lib_nonmember_container_access) ...
+
 #include <cstddef>
 
 namespace boost {
@@ -28,4 +40,6 @@ size(T(&)[N]) noexcept
 
 } /* boost */
 
+#endif // (defined(__cpp_lib_nonmember_container_access) ...
+
 #endif

test/Jamfile.v2

@@ -416,6 +416,7 @@ run span_constexpr_test.cpp ;
 run as_bytes_test.cpp ;
 run as_writable_bytes_test.cpp ;
 compile span_boost_begin_test.cpp ;
+compile span_nonmem_data_size_test.cpp ;
 run make_span_test.cpp ;
 
 run splitmix64_test.cpp

test/data_test.cpp

@@ -9,6 +9,7 @@ Distributed under the Boost Software License, Version 1.0.
 #if !defined(BOOST_NO_CXX11_CONSTEXPR) && !defined(BOOST_NO_CXX11_DECLTYPE)
 #include <boost/core/data.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <iterator>
 
 class range {
 public:
@@ -52,12 +53,28 @@ void test_initializer_list()
     BOOST_TEST_EQ(boost::data(l), l.begin());
 }
 
+void test_ambiguity_with_std_data()
+{
+// Note: This preprocessor check should be equivalent to that in boost/core/data.hpp
+#if (defined(__cpp_lib_nonmember_container_access) && (__cpp_lib_nonmember_container_access >= 201411l)) || \
+    (defined(_MSC_VER) && (_MSC_VER >= 1900))
+
+    // https://github.com/boostorg/core/issues/206
+    range c;
+    using std::data;
+    using boost::data;
+    BOOST_TEST_EQ(data(c), c.data());
+
+#endif
+}
+
 int main()
 {
     test_range();
     test_const_range();
     test_array();
     test_initializer_list();
+    test_ambiguity_with_std_data();
     return boost::report_errors();
 }
 #else

test/size_test.cpp

@@ -9,6 +9,7 @@ Distributed under the Boost Software License, Version 1.0.
 #if !defined(BOOST_NO_CXX11_CONSTEXPR) && !defined(BOOST_NO_CXX11_DECLTYPE)
 #include <boost/core/size.hpp>
 #include <boost/core/lightweight_test.hpp>
+#include <iterator>
 
 struct range {
     std::size_t size() const {
@@ -28,10 +29,26 @@ void test_array()
     BOOST_TEST_EQ(boost::size(a), 4);
 }
 
+void test_ambiguity_with_std_size()
+{
+// Note: This preprocessor check should be equivalent to that in boost/core/size.hpp
+#if (defined(__cpp_lib_nonmember_container_access) && (__cpp_lib_nonmember_container_access >= 201411l)) || \
+    (defined(_MSC_VER) && (_MSC_VER >= 1900))
+
+    // https://github.com/boostorg/core/issues/206
+    range c;
+    using std::size;
+    using boost::size;
+    BOOST_TEST_EQ(size(c), c.size());
+
+#endif
+}
+
 int main()
 {
     test_range();
     test_array();
+    test_ambiguity_with_std_size();
     return boost::report_errors();
 }
 #else

test/span_nonmem_data_size_test.cpp

@@ -0,0 +1,44 @@
+/*
+ *             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)
+ */
+/*
+ * The test verifies that unqualified calls to data() and size()
+ * don't cause ambiguity between std:: and boost:: implementations.
+ * The ambiguity used to be caused by ADL bringing boost::data()/size()
+ * due to namespace of boost::span and a using-declaration of
+ * std::data()/size().
+ *
+ * https://github.com/boostorg/core/issues/206
+ */
+
+#include <boost/config.hpp>
+
+#if !defined(BOOST_NO_CXX11_CONSTEXPR) && !defined(BOOST_NO_CXX11_DECLTYPE)
+
+#include <boost/core/span.hpp>
+#include <iterator>
+
+// Note: This preprocessor check should be equivalent to those in boost/core/data.hpp and boost/core/size.hpp
+#if (defined(__cpp_lib_nonmember_container_access) && (__cpp_lib_nonmember_container_access >= 201411l)) || \
+    (defined(_MSC_VER) && (_MSC_VER >= 1900))
+
+#include <boost/core/data.hpp>
+#include <boost/core/size.hpp>
+
+int* test_data_ambiguity(boost::span<int> sp)
+{
+    using std::data;
+    return data(sp);
+}
+
+boost::span<int>::size_type test_size_ambiguity(boost::span<int> sp)
+{
+    using std::size;
+    return size(sp);
+}
+
+#endif // (defined(__cpp_lib_nonmember_container_access) ...
+#endif // !defined(BOOST_NO_CXX11_CONSTEXPR) && !defined(BOOST_NO_CXX11_DECLTYPE)