c# - 有没有一种方法可以让 switch 使用 C# 8 switch 表达式返回字符串值？

Question

我有这段代码，其中开关的每个部分都向 ModeMessage2 返回一个值。是否可以使用新的 C# switch 表达式(或任何其他代码优化)来优化此 switch 的工作方式？

switch (Settings.Mode)
{
    case MO.Learn:
        ModeMessage2 =
            "Use this mode when you are first learning the phrases and their meanings.";
        if (Settings.Cc == CC.H)
        {
            Settings.Cc = CC.JLPT5;
            App.cardSetWithWordCount = null;
            App.DB.RemoveSelected();
        }
        break;
    case MO.Practice:
        ModeMessage2 =
             "Use this mode to help you memorize the phrases and their meanings.";
        if (Settings.Cc == CC.H)
        {
            Settings.Cc = CC.JLPT5;
            App.cardSetWithWordCount = null;
            App.DB.RemoveSelected();
        }
        break;
    case MO.Quiz:
        if (Settings.Cc == CC.H)
        {
            Settings.Cc = CC.JLPT5;
            App.cardSetWithWordCount = null;
            App.DB.RemoveSelected();
        }
        App.DB.UpdSet(SET.Adp, false);
        ModeMessage2 =
            "Use this mode to run a self marked test.";
        break;
}

Answer 1

您的代码类似于以下内容，但如果设置 ModeMessage2 或其他属性有副作用，那么事情发生的顺序可能很重要，在这种情况下，这在技术上不是 100% 等效的。

IList<MO> specialModes = new[] { MO.Learn, MO.Practice, MO.Quiz };

if (specialModes.Contains(Settings.Mode) && Settings.Cc == CC.H) {
   Settings.Cc = CC.JLPT5;
   App.cardSetWithWordCount = null;
   App.DB.RemoveSelected();
}

ModeMessage2 = Settings.Mode switch {
   MO.Learn => "Use this mode when you are first learning the phrases and their meanings.",
   MO.Practice => "Use this mode to help you memorize the phrases and their meanings.",
   MO.Quiz => "Use this mode to run a self marked test.",
   _ => "Unknown mode value" // or throw
};

if (Settings.Mode == MO.Quiz)
   App.DB.UpdSet(SET.Adp, false);