4 ms·

Another use of std::monostate is as a special "unset/don't care" value for a template parameter. eg template<typename T = std::monostate> class C {

Another use of std::monostate is as a special "unset/don't care" value for a template parameter. eg template<typename T = std::monostate> class C { ... if constexpr (!std::is_same_v<T, std::monostate> { // T-related behaviour here } };

klyrs 2y ago
I greatly prefer tag classes for this. You can define 'em in a single line and a downstream user can't accidentally plug the unset value in to the template.
ot 2y ago
You can use void for that.
- Maxatar 2y ago
  void could be an actual meaningful type for a template rather than a dummy type.
  - ot 2y ago
    You could say the same thing about std::monostate, which is not a dummy type. If you need a unique sentinel type you have to make one for that purpose.