Add support for socket_ref to multipart_t ctor/send/recv (#487)

* Add support for socket_ref to multipart_t ctor/send/recv

Fixes #448

tests/multipart.cpp

@@ -2,6 +2,22 @@
 #include <zmq_addon.hpp>
 
 #ifdef ZMQ_HAS_RVALUE_REFS
+
+#ifdef ZMQ_CPP17
+static_assert(std::is_invocable<decltype(&zmq::multipart_t::send),
+                                zmq::multipart_t *,
+                                zmq::socket_ref,
+                                int>::value,
+              "Can't multipart_t::send with socket_ref");
+static_assert(std::is_invocable<decltype(&zmq::multipart_t::recv),
+                                zmq::multipart_t *,
+                                zmq::socket_ref,
+                                int>::value,
+              "Can't multipart_t::recv with socket_ref");
+#endif
+static_assert(std::is_constructible<zmq::multipart_t, zmq::socket_ref>::value,
+              "Can't construct with socket_ref");
+
 /// \todo split this up into separate test cases
 ///
 TEST_CASE("multipart legacy test", "[multipart]")

zmq_addon.hpp

@@ -331,7 +331,7 @@ class multipart_t
     multipart_t() {}
 
     // Construct from socket receive
-    multipart_t(socket_t &socket) { recv(socket); }
+    multipart_t(socket_ref socket) { recv(socket); }
 
     // Construct from memory block
     multipart_t(const void *src, size_t size) { addmem(src, size); }
@@ -393,7 +393,7 @@ class multipart_t
     bool empty() const { return m_parts.empty(); }
 
     // Receive multipart message from socket
-    bool recv(socket_t &socket, int flags = 0)
+    bool recv(socket_ref socket, int flags = 0)
     {
         clear();
         bool more = true;
@@ -413,7 +413,7 @@ class multipart_t
     }
 
     // Send multipart message to socket
-    bool send(socket_t &socket, int flags = 0)
+    bool send(socket_ref socket, int flags = 0)
     {
         flags &= ~(ZMQ_SNDMORE);
         bool more = size() > 0;