C# 8 switch 表达式，具有相同结果的多个案例

Question

如何编写 switch 表达式以支持返回相同结果的多种情况？

对于版本 8 之前的 C#，开关可以这样写:

var switchValue = 3;
var resultText = string.Empty;
switch (switchValue)
{
    case 1:
    case 2:
    case 3:
        resultText = "one to three";
        break;
    case 4:
        resultText = "four";
        break;
    case 5:
        resultText = "five";
        break;
    default:
        resultText = "unkown";
        break;
}

当我使用 C# 版本 8 时，表达式语法是这样的:

var switchValue = 3;
var resultText = switchValue switch
{
    1 => "one to three",
    2 => "one to three",
    3 => "one to three",
    4 => "four",
    5 => "five",
    _ => "unknown",
};

所以我的问题是:如何将案例 1、2 和 3 变成一个 switch-case-arm，这样值就不需要重复了？

根据“Rufus L”的建议更新:

对于我给出的示例，这是可行的。

var switchValue = 3;
var resultText = switchValue switch
{
    var x when (x >= 1 && x <= 3) => "one to three",
    4 => "four",
    5 => "five",
    _ => "unknown",
};

但这并不是我想要完成的。这仍然只是一种情况(具有过滤条件)，而不是产生相同右侧结果的多种情况。

Answer 1

C# 9 支持以下内容:

var switchValue = 3;
var resultText = switchValue switch
{
    1 or 2 or 3 => "one, two, or three",
    4 => "four",
    5 => "five",
    _ => "unknown",
};

或者:

var switchValue = 3;
var resultText = switchValue switch
{
    >= 1 and <= 3 => "one, two, or three",
    4 => "four",
    5 => "five",
    _ => "unknown",
};

Source

---

对于旧版本的 C#，我使用以下扩展方法:

public static bool In<T>(this T val, params T[] vals) => vals.Contains(val);

像这样:

var switchValue = 3;
var resultText = switchValue switch
{
    var x when x.In(1, 2, 3) => "one, two, or three",
    4 => "four",
    5 => "five",
    _ => "unknown",
};

比when x == 1 || 更简洁一点x == 2 || x == 3 并且比 when new [] {1, 2, 3}.Contains(x) 具有更自然的顺序。