Re: [Describe] Review - Part 1: Enumerators

From: Peter Dimov (pdimov_at_[hidden])
Date: 2021-03-10 17:57:30

Andrzej Krzemienski wrote:
> I do not appreciate the BOOST_DEFINE_ macros for enumerations. We get as
> much as four of them, ...

We'll even get eight once the requested support for class-nested enums is added. :-)

> and neither is able to handle the use case that I consider
> basic, which I often have in my code: where I omit value zero and start from 1:
> 
> struct Error {
>   badSoething = 1,
>   badSomethingElse,
>   tooLongSomethng,
>   ...
> };
> 
> So, I am not sure how many real life enums these macros cover.

They cover the common case of an enumeration without any initializers; the
case where you have a number of alternatives but don't care about their exact
numeric values. I do believe this is reasonably common, even if it's not
universal.

E.g. enum class Shape { Triangle, Rectangle, Circle }.

Further e.g.

template<class E, class... T> class evariant: public variant<T...>
{
public:

    E index() const { return (E)variant<T...>::index(); }
};

and then evariant<Shape, Triangle, Rectangle, Circle>, and JSON serialization
gives you ["Circle", {"radius": 14.2}]. Or perhaps {"Circle": {"radius": 14.2}}. :-)