C++20范围从枚举

Question

枚举可以用作(或转换为) C++20范围吗？

我正在考虑以下用例，cartesian_product()是C++23的不幸之处：

#include <algorithm>
using namespace std::ranges;

enum Fruit{APPLE, STRAWBERRY, COCONUT};
enum Vegetable{CARROT,POTATOE};
    
for (auto [fruit, vegetable] : views::cartesian_product(Fruit, Vegetable))
{
...
}

Answer 1

您可以这样做，只是需要一个库的帮助才能将枚举转换为一系列枚举数名称。其中一个类库是Boost.Describe。

#include <array>
#include <boost/describe.hpp>
#include <fmt/ranges.h>

enum Fruit{APPLE, STRAWBERRY, COCONUT};
enum Vegetable{CARROT,POTATO};

BOOST_DESCRIBE_ENUM(Fruit, APPLE, STRAWBERRY, COCONUT);
BOOST_DESCRIBE_ENUM(Vegetable, CARROT, POTATO);

template<class E>
constexpr auto enum_names() {
    return []<template <class...> class L, class... T>(L<T...>)
        -> std::array<char const*, sizeof...(T)>
    {
        return {T::name...};
    }(boost::describe::describe_enumerators<E>());
}

int main() {
    // prints fruits=["APPLE", "STRAWBERRY", "COCONUT"] vegetables=["CARROT", "POTATO"]
    fmt::print("fruits={} vegetables={}\n", enum_names<Fruit>(), enum_names<Vegetable>());
}

演示