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

This avoids the potential ambiguity between boost:: and std:: functions
when the user calls data() or size() unqualified and both alternatives
are found via ADL.

Refs https://github.com/boostorg/core/issues/206.

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/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