The function you're calling is non-const. Call the following const version instead.
DisplayRulePtrVector const& displayRules = displayRuleSetCP->GetDisplayRulesC();
Please don't modify the DisplayRule objects contained in the returned vector.
DisplayRulePtrVector const& displayRules = displayRuleSetCP->GetDisplayRulesC();
Please don't modify the DisplayRule objects contained in the returned vector.