Fix type concept check. Remove refernce to get key_type et al

include/jwt/detail/meta.hpp

@@ -31,7 +31,7 @@ struct empty_type {};
 /**
  */
 template <typename T, typename=void>
-struct has_create_json_obj_member: std::false_type
+struct has_create_json_obj_member
 {
 };
 
@@ -72,22 +72,21 @@ template <typename T>
 struct is_mapping_concept<T,
   void_t<
     typename std::enable_if<
-      std::is_constructible<jwt::string_view, typename T::key_type>::value,
+      std::is_constructible<jwt::string_view, typename std::remove_reference_t<T>::key_type>::value,
       void
     >::type,
 
     typename std::enable_if<
-      std::is_constructible<jwt::string_view, typename T::mapped_type>::value,
+      std::is_constructible<jwt::string_view, typename std::remove_reference_t<T>::mapped_type>::value,
       void
     >::type,
 
     decltype(
-      std::declval<T&>().operator[](std::declval<const typename T::key_type&>()),
+      std::declval<T&>().operator[](std::declval<typename std::remove_reference_t<T>::key_type>()),
       std::declval<T&>().begin(),
       std::declval<T&>().end(),
       (void)0
     )
-
   >
   >: std::true_type
 {

include/jwt/parameters.hpp

@@ -107,16 +107,6 @@ struct headers_param
 using param_init_list_t = std::initializer_list<std::pair<jwt::string_view, jwt::string_view>>;
 
 
-/**
- */
-template <typename MappingConcept,
-          typename=typename jwt::detail::meta::is_mapping_concept<MappingConcept>::type>
-detail::payload_param<MappingConcept> 
-payload(MappingConcept&& mc)
-{
-  return { std::forward<MappingConcept>(mc) };
-}
-
 /**
  */
 detail::payload_param<std::unordered_map<std::string, std::string>>
@@ -131,6 +121,18 @@ payload(const param_init_list_t& kvs)
   return { std::move(m) };
 }
 
+/**
+ */
+template <typename MappingConcept>
+detail::payload_param<MappingConcept>
+payload(MappingConcept&& mc)
+{
+  static_assert (jwt::detail::meta::is_mapping_concept<MappingConcept>::value,
+      "Template parameter does not meet the requirements for MappingConcept.");
+
+  return { std::forward<MappingConcept>(mc) };
+}
+
 
 /**
  */
@@ -153,16 +155,6 @@ detail::algorithm_param algorithm(jwt::algorithm alg)
   return { alg };
 }
 
-/**
- */
-template <typename MappingConcept,
-          typename=typename jwt::detail::meta::is_mapping_concept<MappingConcept>::type>
-detail::headers_param<MappingConcept>
-headers(MappingConcept&& mc)
-{
-  return { std::forward<MappingConcept>(mc) };
-}
-
 /**
  */
 detail::headers_param<std::map<std::string, std::string>>
@@ -177,6 +169,18 @@ headers(const param_init_list_t& kvs)
   return { std::move(m) };
 }
 
+/**
+ */
+template <typename MappingConcept>
+detail::headers_param<MappingConcept>
+headers(MappingConcept&& mc)
+{
+  static_assert (jwt::detail::meta::is_mapping_concept<MappingConcept>::value,
+       "Template parameter does not meet the requirements for MappingConcept.");
+
+  return { std::forward<MappingConcept>(mc) };
+}
+
 } // END namespace params
 } // END namespace jwt
 

include/jwt/test/test_jwt_object.cc

@@ -11,12 +11,14 @@ void basic_jwt_object_test()
                                 {"a", "b"},
                                 {"c", "d"} 
                               }));
+
   //check with std::map
   std::map<std::string, std::string> m;
   m["a"] = "b";
   m["c"] = "d";
 
   jwt::jwt_object obj1{payload(m)};
+  
   auto obj2 = std::move(obj1);
 
   std::cout << obj2.payload() << std::endl;