是否可以在 C++ 的变量中保存多种类型的枚举？

Question

Is it possible to do something like this in C++:

enum A {//Starts from 0 and has no enum with out of place value like 0,1,5,40, etc.
    eg1,
    eg2,
    eg3,
    ...
}

enum B {//Same structure as enum A
    e1,
    e2,
    e3,
    ...
}

some_data_type e = eg1;//No errors here
e = e2;//No errors here

I think it could be something like just an integer, but just to be safe is there another way to do this?

Answer 1

In C++17 and later, you can use std::variant for that:

enum A {//Starts from 0 and has no enum with out of place value like 0,1,5,40, etc.
    eg1,
    eg2,
    eg3,
    ...
}

enum B {//Same structure as enum A
    e1,
    e2,
    e3,
    ...
}

std::variant<A,B> e = eg1;
e = e2;

Answer 2

If you're ok losing the distinction between the original types, then an integer would work. If you want to be a little more restrictive and only allow assignment from and comparison against "compatible" enums, then a user-defined type with implicit conversion from both A and B is probably wanted. Unfortunately you can't add conversions directly between two enums because conversion functions and converting constructors both have to be member functions, which enums don't allow.

If you want to keep them distinguished later, then boost::variant<A, B> will do that.