Assertion and constexpr improvements for str_buffer

Author: gummif

tests/buffer.cpp

@@ -244,7 +244,7 @@ TEST_CASE("const_buffer creation with str_buffer", "[buffer]")
     CHECK(b.data() == static_cast<const wchar_t*>(wd));
 
     zmq::const_buffer b2_null = zmq::buffer("hello");
-    zmq::const_buffer b2 = zmq::str_buffer("hello");
+    constexpr zmq::const_buffer b2 = zmq::str_buffer("hello");
     CHECK(b2_null.size() == 6);
     CHECK(b2.size() == 5);
     CHECK(std::string(static_cast<const char*>(b2.data()), b2.size()) == "hello");

zmq.hpp

@@ -1114,12 +1114,13 @@ const_buffer buffer(std::basic_string_view<T, Traits> data, size_t n_bytes) noex
 // where the buffer size excludes the terminating character.
 // Equivalent to zmq::buffer(std::string_view("...")).
 template<class Char, size_t N>
-const_buffer str_buffer(const Char (&data)[N]) noexcept
+constexpr const_buffer str_buffer(const Char (&data)[N]) noexcept
 {
     static_assert(detail::is_pod_like<Char>::value, "Char must be POD");
-    static_assert(N > 0, "N > 0");
+#ifdef ZMQ_CPP14
     assert(data[N - 1] == Char{0});
-    return const_buffer(N == 1 ? nullptr : static_cast<const Char*>(data), 
+#endif
+    return const_buffer(static_cast<const Char*>(data), 
                         (N - 1) * sizeof(Char));
 }