使用类包装枚举
字数统计：440
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C++ 中的枚举类提供了一种定义常量的方式，但直接使用枚举往往存在表达能力不足的问题，导致用户使用繁琐，因此使用类对枚举进行包装是常见的方式，使得枚举可以拥有自定义的继承关系和转换规则，这种手法也在 std::<partical | strong | weak>_ordering 中得到运用。
#include <cassert>
class State {
enum class State_impl :unsigned char {
Ready, Active, Suspended, Successed, Failed
};
State_impl state = State_impl::Ready;
State() = delete;
constexpr State(State_impl state) { this->state = state; }
public:
constexpr explicit operator int() const {
return static_cast<int>(state);
}
constexpr State& operator=(int state) {
bool check = false;
State_impl state_impl = static_cast<State_impl>(state);
switch (state_impl) {
case State_impl::Ready:
case State_impl::Active:
case State_impl::Suspended:
case State_impl::Successed:
case State_impl::Failed:
check = true;
}
assert(check);
this->state = static_cast<State_impl>(state);
return *this;
}
const static State Ready;
const static State Active;
const static State Suspended;
const static State Successed;
const static State Failed;
};
inline constexpr State State::Ready{ State_impl::Ready };
inline constexpr State State::Active{ State_impl::Active };
inline constexpr State State::Suspended{ State_impl::Suspended };
inline constexpr State State::Successed{ State_impl::Successed };
inline constexpr State State::Failed{ State_impl::Failed };
int main() {
int a{ State::Suspended };
a = static_cast<int>(State::Suspended);
State state = State::Ready;
state = a;
}