切换大小写，检查 C# 3.5 中的范围 [英] Switch case, check ranges in C# 3.5

问题描述

在 C# 中，switch 语句不允许 case 跨越值的范围.我不喜欢为此使用 if-else 循环的想法，那么还有其他方法可以检查 C# 中的数字范围吗?

In C#, the switch statement doesn't allow cases to span ranges of values. I don't like the idea of using if-else loops for this purpose, so are there any other ways to check numeric ranges in C#?

推荐答案

可以使用一个HashTable分别Dictionary来创建Condition =>的映射；动作.

You can use a HashTable respectively Dictionary to create a mapping of Condition => Action.

例子:

class Programm
{
    static void Main()
    {
        var myNum = 12;

        var cases = new Dictionary<Func<int, bool>, Action>
        { 
            { x => x < 3 ,    () => Console.WriteLine("Smaller than 3")   } ,
            { x => x < 30 ,   () => Console.WriteLine("Smaller than 30")  } ,
            { x => x < 300 ,  () => Console.WriteLine("Smaller than 300") } 
        };

        cases.First(kvp => kvp.Key(myNum)).Value();
    }
}

这种技术是 switch 的一般替代方法，尤其是当操作仅包含一行时(如方法调用).

This technique is a general alternative to switch, especially if the actions consists only of one line (like a method call).

如果你喜欢类型别名:

using Int32Condition = System.Collections.Generic.Dictionary<System.Func<System.Int32, System.Boolean>, System.Action>;
...
    var cases = new Int32Condition()
    { 
        { x => x < 3 ,    () => Console.WriteLine("Smaller than 3")   } ,
        { x => x < 30 ,   () => Console.WriteLine("Smaller than 30")  } ,
        { x => x < 300 ,  () => Console.WriteLine("Smaller than 300") } 
    };

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