Merge pull request #345 from redboltz/added_has_as_to_pair

Added has_as SFINAE.

Author: nobu-k

include/msgpack/adaptor/pair.hpp

@@ -20,6 +20,8 @@
 
 #include "msgpack/versioning.hpp"
 #include "msgpack/adaptor/adaptor_base.hpp"
+#include "msgpack/meta.hpp"
+
 #include <utility>
 
 namespace msgpack {
@@ -33,7 +35,8 @@ namespace adaptor {
 #if !defined(MSGPACK_USE_CPP03)
 
 template <typename T1, typename T2>
-struct as<std::pair<T1, T2>> {
+struct as<std::pair<T1, T2>,
+          typename std::enable_if<msgpack::all_of<msgpack::has_as, T1, T2>::value>::type> {
     std::pair<T1, T2> operator()(msgpack::object const& o) const {
         if (o.type != msgpack::type::ARRAY) { throw msgpack::type_error(); }
         if (o.via.array.size != 2) { throw msgpack::type_error(); }