fix typo and make alert non-copyable

include/libtorrent/alert.hpp

@@ -80,6 +80,9 @@ POSSIBILITY OF SUCH DAMAGE.
 namespace libtorrent {
 
 	// The ``alert`` class is the base class that specific messages are derived from.
+	// alert types are not copyable, and cannot be constructed by the client. The
+	// pointers returned by libtorrent are short lived (the details are described
+	// under session_handle::pop_alerts())
 	class TORRENT_EXPORT alert
 	{
 	public:
@@ -283,10 +286,10 @@ namespace libtorrent {
 #endif // TORRENT_NO_DEPRECATE
 
 	protected:
+		// the alert is not copyable (but for backwards compatibility reasons it
+		// retains the ability to clone itself, for now).
 #if __cplusplus >= 201103L
-		alert(alert const&) = default;
-#else
-		alert(alert const&);
+		alert(alert const& rhs) = default;
 #endif
 
 	private:

include/libtorrent/alert_types.hpp

@@ -163,7 +163,25 @@ namespace libtorrent
 	#define TORRENT_CLONE(name)
 #endif
 
+	// we can only use = default in C++11
+	// the purpose of this is just to make all alert types non-copyable from user
+	// code. The heterogeneous queue does not yet have an emplace_back(), so it
+	// still needs to copy alerts, but the important part is that it's not
+	// copyable for clients.
+	// TODO: Once the backwards compatibility of clone() is removed, and once
+	// C++11 is required, this can be simplified to just say = delete
+#if __cplusplus >= 201103L
+	#define TORRENT_PROTECTED_CCTOR(name) \
+	protected: \
+		template <class T> friend struct heterogeneous_queue; \
+		name(name const&) = default; \
+	public:
+#else
+	#define TORRENT_PROTECTED_CCTOR(name)
+#endif
+
 #define TORRENT_DEFINE_ALERT_IMPL(name, seq, prio) \
+	TORRENT_PROTECTED_CCTOR(name) \
 	static const int priority = prio; \
 	static const int alert_type = seq; \
 	virtual int type() const TORRENT_OVERRIDE { return alert_type; } \