Throw on missing non-optional object key

code/json/marshaling.hxx

@@ -3,6 +3,7 @@
 
 #include <code/json/optional.hxx>
 #include <code/json/pointer.hxx>
+#include <code/json/traits.hxx>
 #include <code/json/variant.hxx>
 
 #include <chrono>
@@ -41,11 +42,17 @@ namespace code::json
       std::copy_n(str, N, name);
     }
 
-    operator std::string const() const
+    std::string const
+    str() const
     {
       return name;
     }
 
+    operator std::string const() const
+    {
+      return str();
+    }
+
     char name[N];
 
   };
@@ -67,6 +74,10 @@ namespace code::json
     using T = member_traits<decltype(Member)>::class_type;
     using M = member_traits<decltype(Member)>::member_type;
 
+    static constexpr bool is_optional{
+      is_optional_v<M>
+    };
+
     static
     void
     marshal(variant& v, T const& instance, marshaling_context_t* context)
@@ -78,11 +89,22 @@ namespace code::json
     void
     unmarshal(T& instance, variant const& v, marshaling_context_t* context)
     {
+      if (!v.contains(Name.str())) {
+        if (is_optional) {
+          return;
+        }
+
+        throw std::runtime_error{"missing field '" + Name.str() + "'"};
+      }
+
       instance.*Member = marshaling_traits<M>::unmarshal(v.get(Name), context);
     }
 
     struct pointer_t
     {
+      using T = member_traits<decltype(Member)>::class_type;
+      using M = member_traits<decltype(Member)>::member_type;
+
       static pointer const&
       ptr()
       {
@@ -104,6 +126,10 @@ namespace code::json
         auto ptr_v = ptr().read(v);
 
         if (!ptr_v) {
+          if (is_optional) {
+            return;
+          }
+
           throw std::runtime_error{ "missing field '" + to_string(ptr()) + "'" };
         }