Added static_asserts to make sure that only tables can be used as roo…

…t elements

include/rfl/toml/Writer.hpp

@@ -37,22 +37,23 @@ class Writer {
 
   ~Writer() = default;
 
-  OutputArrayType array_as_root(const size_t _size) const noexcept {
-    value_as_root(_size);
+  template <class T>
+  OutputArrayType array_as_root(const T _size) const noexcept {
+    static_assert(rfl::always_false_v<T>,
+                  "TOML only allows tables as the root element.");
     return OutputArrayType{nullptr};
   }
 
   OutputObjectType object_as_root(const size_t _size) const noexcept {
     return OutputObjectType{root_};
   }
 
-  OutputVarType null_as_root() const noexcept { return value_as_root(0); }
+  OutputVarType null_as_root() const noexcept { return OutputVarType{}; }
 
   template <class T>
   OutputVarType value_as_root(const T& _var) const noexcept {
-    // TODO
-    // static_assert(rfl::always_false_v<T>,
-    //              "TOML only allows tables as its root.");
+    static_assert(rfl::always_false_v<T>,
+                  "TOML only allows tables as the root element.");
     return OutputVarType{};
   }