c++ - 您如何将所有枚举常量纳入范围？

Question

有没有办法将所有枚举 constants 纳入范围？我不是指类型，我指的是常量本身。

struct Foo {
    enum Bar {
        A = 1, B = 2, C = 4, D = 8
    };
};

int main() {
    using E = Foo;
    int v = E::A | E::B | E::C | E::D;

    // But is it possible to instead do...
    using Foo::Bar::*; // (not real C++)
    int v = A|B|C|D; // <-- all enum constants are brought into scope
}

Answer 1

// This already works, of course.
using E = Foo;
Foo::Bar v = E::A | E::B | E::C | E::D;

嗯，不是真的，因为 E::A | E::B | E::C | E::D 是一个 int 和 you can't implicitly convert an int to an enum .

但这并不能阻止您使用 c++20的使用枚举(除非你不能使用C++20):

struct Foo {
    enum Bar {
        A = 1, B = 2, C = 4, D = 8
    };
};

int main() {
    using enum Foo::Bar; // (real C++20!)
    Foo::Bar v = D; 
}