DynMathObject: get_name(): return non-empty name in more cases

when the equation is syntactically valid but has errors
of other kinds (e.g. undefined variable or function)

include/zecalculator/math_objects/decl/dyn_math_object.h

@@ -73,7 +73,8 @@ class DynMathObject: public tl::expected<MathObjectsVariant<type>, Error>
     requires (std::is_convertible_v<DBL, double> and ...)
   tl::expected<double, Error> evaluate(DBL... val) const;
 
-  /// @brief returns the name of the object, if it's valid, otherwise empty string
+  /// @brief returns the name of the object
+  /// @note returns non-empty string only if this instance contains a syntactically valid equation or object
   std::string_view get_name() const;
 
   /// @brief gets the value of the expected (the variant) as a specific alternative

include/zecalculator/math_objects/impl/dyn_math_object.h

@@ -350,7 +350,9 @@ bool DynMathObject<type>::holds() const
 template <parsing::Type type>
 std::string_view DynMathObject<type>::get_name() const
 {
-  if (bool(*this))
+  if (opt_eq_object)
+    return opt_eq_object->name;
+  else if (bool(*this))
     return std::visit([](const auto& val){ return val.get_name(); }, **this);
   else return std::string_view();
 }

test/function_test.cpp

@@ -330,4 +330,16 @@ int main()
 
   } | std::tuple<FAST_TEST, RPN_TEST>{};
 
+  "name of function in error state"_test = []<class StructType>()
+  {
+    constexpr parsing::Type type = std::is_same_v<StructType, FAST_TEST> ? parsing::Type::FAST : parsing::Type::RPN;
+
+    MathWorld<type> world;
+
+    auto& f = world.new_object() = "f( x)  = cos(x) * g(X)";
+
+    expect(f.get_name() == "f");
+
+  } | std::tuple<FAST_TEST, RPN_TEST>{};
+
 }