util/SpanCast: add ReferenceAsBytes()

src/io/BufferedOutputStream.hxx

@@ -51,7 +51,7 @@ public:
 	 */
 	template<typename T>
 	void WriteT(const T &value) {
-		Write(std::as_bytes(std::span{&value, 1}));
+		Write(ReferenceAsBytes(value));
 	}
 
 	/**

src/output/plugins/snapcast/Client.cxx

@@ -105,7 +105,7 @@ template<typename T>
 static bool
 SendT(SocketDescriptor s, const T &buffer) noexcept
 {
-	return Send(s, std::as_bytes(std::span{&buffer, 1}));
+	return Send(s, ReferenceAsBytes(buffer));
 }
 
 static bool

src/util/SpanCast.hxx

@@ -59,6 +59,16 @@ AsBytes(std::string_view sv) noexcept
 	return std::as_bytes(ToSpan(sv));
 }
 
+/**
+ * Cast a reference to a fixed-size std::span<const std::byte>.
+ */
+template<typename T>
+constexpr auto
+ReferenceAsBytes(const T &value) noexcept
+{
+	return std::as_bytes(std::span<const T, 1>{&value, 1});
+}
+
 constexpr std::string_view
 ToStringView(std::span<const char> s) noexcept
 {