add string_view.hh – stolen from pEpMIME. :-D

src/string_view.hh

@@ -0,0 +1,41 @@
+// This file is under GNU General Public License 3.0
+// see LICENSE.txt
+
+#ifndef PEP_DATATYPES_STRING_VIEW_HH
+#define PEP_DATATYPES_STRING_VIEW_HH
+
+#if (__cplusplus >= 201606)  // std::string_view is C++17.
+#   include <string_view>
+
+namespace pEp
+{
+    typedef std::string_view string_view;
+}
+
+#else // in C++11 / C++14 use boost::string_view instead.
+#   include <boost/utility/string_view.hpp>
+
+namespace pEp
+{
+    typedef boost::string_view string_view;
+
+    // boost::string_view does not provide these operations, neither by boost nor by the stdlib. :-(
+    inline
+    std::string& operator+=(std::string& s, const string_view v)
+    {
+        s.append(v.data(), v.size());
+        return s;
+    }
+
+    inline
+    std::string operator+(std::string s, const string_view v)
+    {
+        return s += v;
+    }
+    
+    using ::operator+=;
+} // end of namespace pEp
+
+#endif // C++17 switch
+
+#endif // PEP_DATATYPES_CONFIG_HH