Things C++ 20 Deliberately Broke

[Ola Fosheim Grøstad]

On Tuesday, 27 September 2022 at 01:54:19 UTC, Steven 
Schveighoffer wrote:
> I misremembered how enums work in (old) C/C++. But it seems 
> really awkward to make it difficult to extract the real value. 
> I also don't see a huge harm in it implicitly converting, as D 
> has allowed.
>
> I suppose using namespaces and constexpr, one can *almost* 
> mimic the behavior. But it's still not a type.

Hm, do you mean enums or constexpr? Constexpr constants are 
usually put inside a class. So you access them as 
`ClassName::constant_name`. C++20 also allows accessing enums 
through the class scope by allowing the `using` statement to 
apply to enums inside a class definition. So you can certainly 
build an enum like type with more advanced features than regular 
enums in C++. You can do it with enums, or without enums.

You can use enums to create new nominal integers. An example of 
this is std::byte which is defined like this:

```C++
enum class byte : unsigned char {} ;

```

As a result you cannot use operators on a `byte` and you now have 
a type for unassuming octets. You can do this for your own 
integer-based type quite easily and  define the operations you 
want.

> It seems the intuitive behavior is not readily accessible with 
> C++.

The intuitive behaviour for an enumeration are the operations: 
comparison, successor, predecessor.

It gets a bit messier in C/C++ as you also tend to use it for 
bitsets. Which probably should be a different concept. Anyway, 
I've started to use `enum class` for almost everything and then 
define overloaded set-functions that work on them. That way you  
encapsulate the casting and bit manipulation and hopefully get 
fewer bugs as a result.