demonstrate the motivation behind the previous patch

Author: Martin C Drohmann

example/cpp11/non_def_con_class.cpp

@@ -23,6 +23,16 @@ struct my {
     my(int a):a(a) {}
     int a;
     MSGPACK_DEFINE(a);
+
+    bool operator==(const my & other) const
+    {
+       return other.a == a;
+    }
+
+    bool operator<(const my & other) const
+    {
+       return other.a > a;
+    }
 };
 
 namespace msgpack {
@@ -48,4 +58,34 @@ int main() {
     msgpack::object obj(m1, z);
     std::cout << obj << std::endl;
     assert(m1.a == obj.as<my>().a);
+
+    // useful keys for maps do not have as<>() method implemented:
+    std::cout << "has_as<int>    " << msgpack::has_as<int>::value << std::endl;
+    std::cout << "has_as<string> " << msgpack::has_as<std::string>::value << std::endl;
+
+    // BEFORE PATCH: as a result as<map<K, V> >() is not available either.
+    // AFTER PATCH:  as<map<K, V> >() is available if key OR value have an as<>() implementation
+    std::cout << "has_as<std::map<int, my> > " << msgpack::has_as<std::map<int, my> >::value << std::endl;
+
+    std::map<int, my> m;
+    m.emplace(1, my(17));
+    msgpack::object obj2(m, z);
+    std::cout << obj2 << std::endl;
+
+    // BEFORE PATCH: this makes the following break with a compiler error,
+    // beacuse it uses the deleted my:my() constructor, as it falls back to the
+    // convert() method.
+    // AFTER PATCH: the following works and uses the customary as() implementation
+    assert(m == obj2.as<decltype(m)>());
+
+    std::map<my, int> m2;
+    m2.emplace(17, 42);
+    msgpack::object obj3(m2, z);
+    std::cout << obj3 << std::endl;
+
+    // BEFORE PATCH: this makes the following break with a compiler error:
+    // beacuse it uses the deleted my:my() constructor, as it falls back to the
+    // convert() method.
+    // AFTER PATCH: the following works and uses the customary as() implementation
+    assert(m2 == obj3.as<decltype(m2)>());
 }