Re: [Interest] Flags: Non-intrusive, type-safe bitwise operators for enums

On 3/16/26 11:59, Tobias Loew via Boost wrote:
> Key Features:
> 
> * Type-safety: Prevents accidental mixing of different enum types and 
> disables built-in arithmetic operators for enabled enums to turn logical 
> errors into compilation errors.
> * Non-intrusive: Can be opted-in for existing enums (both scoped and 
> unscoped) without modifying their definition. Simple macro-based opt-in 
> via BOOST_FLAGS(...) [currently intended name].
> * Compile-Time Friendly: Everything is constexpr, making it usable in 
> template arguments.
> * Zero Overhead: Designed as zero-cost abstraction in optimized builds.
> * Distinguishes between flag-sets and their negations at the type level 
> (based on a sound mathematical model).
> * Requires at least C++11, uses newer features if present

While better support for bit flags based on scoped enums is undoubtedly 
useful, I don't like how verbose the example code is.

I've considered an alternate solution to the same problem based on a 
wrapper around std::bitset.

   template<typename Enum> class enum_bitset {
   public:
     auto operator[](Enum idx) {
       return this->data_store[static_cast<std::size_t>(idx)];
     }
     // ...and all of the other member functions...
   private:
     std::bitset<...> data_store;
   };

This has the advantage of getting rid of all of the ugly 
boost::flags::nth_bits and boost::flags::anys in the example code:

   enum class pizza_topping { tomato, cheese, salami, olives, garlic };

   void order_pizza(enum_bitset<pizza_topping> const &toppings) {
     std::cout << "Pizza ordered with\n";
     if (toppings[pizza_toppings::tomato]) {
         std::cout << "- tomato\n";
     }
     if (toppings[pizza_toppings::cheese]) {
         std::cout << "- cheese\n";
     }
     if (toppings[pizza_toppings::salami]) {
         std::cout << "- salami\n";
     }
     if (toppings[pizza_toppings::olives]) {
         std::cout << "- olives\n";
     }
     if (toppings[pizza_toppings::garlic]) {
         std::cout << "- garlic\n";
     }
     std::cout << "\n";
   }

Isn't that so much more readable and compact?


-- 
Rainer Deyke - [email protected]

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