在 Go 中使用位掩码（使用 iota 进行 Go 枚举）

Question

有点卡住了。

我正在尝试弄清楚如何使用 go 枚举从 const 获取位掩码值。例如，如果密钥为 5，即 0101 位，则将是狗和鱼。获取位值（1、2、4、8、16、32、64 等）以便我可以选择字符串值并返回动物集的最简单方法是什么？

type Key int

const (
    Dog Key = 1 << iota
    Cat
    Fish
    Horse
    Snake
    Rabbit
    Lion
    Rino
    Hedgehog
)

一直在阅读，但我无法解决这个问题。

Answer 1

Declare a slice of strings where the strings correspond to the constant names:

var animalNames = []string{
    "Dog",
    "Cat",
    "Fish",
    "Horse",
    "Snake",
    "Rabbit",
    "Lion",
    "Rino",
    "Hedgehog",
}

To get the names for the bits, loop through the names. If the corresponding bit is set, add the name to the result:

func Names(k Key) []string {
    var result []string
    for i := 0; i < len(animalNames); i++ {
        if k&(1<<uint(i)) != 0 {
            result = append(result, animalNames[i])
        }
    }
    return result
}

Run it on the playground.

If you change the the constants to be bit indexes instead of bit values, then you can use the stringer utility to create a func (k Key) String() string. Here's the code for this change:

type Key uint

const (
    Dog Key = iota
    Cat
    Fish
    Horse
    Snake
    Rabbit
    Lion
    Rino
    Hedgehog
)

//go:generate stringer -type=Key

func Names(k Key) []string {
    var result []string
    for animal := Dog; animal <= Hedgehog; animal++ {
        if k&(1<<animal) != 0 {
            result = append(result, animal.String())
        }
    }
    return result
}