C# 多个开关情况相同的值 lambda 语法

Question

可以这样转换:

int x = 1;
string xString;
switch (x)
{
    case 1:
        xString = "1";
        break;
    case 2:
        xString = "2";
        break;
    default:
        xString = "default";
        break;
}
Console.WriteLine(xString);

进入这个:

int x = 1;
string xString = x switch
{
    1 => "1",
    2 => "2",
    _ => "default",
};
Console.WriteLine(xString);

但是，在多个情况下将 xString 的值设置为相同值而不为每种情况创建 lambda 行的语法是什么？

int x = 1;
string xString;
switch (x)
{
    case 1:
        xString = "1";
        break;
    case 2:
    case 4:
        xString = "even numbers";
        break;
    default:
        xString = "default";
        break;
}
Console.WriteLine(xString);

Answer 1

不幸的是，您不能使用范围，但您可以使用 when .

str = i switch
{
    int n when (n >= 100) => "asd1",
    int n when (n < 100 && n >= 50) => "asd2",
    int n when (n < 50) => "asd3",
    _ => str
};

或丢弃和隐式引用

str = i switch
{
   _ when i >= 100 => "asd1",
   _ when i < 100 && i >= 50 => "asd2",
   _ when i < 50 => "asd3",
   _ => str
};

switch (C# reference)

Starting with C# 7.0, because case statements need not be mutuallyexclusive, you can add a when clause to specify an additionalcondition that must be satisfied for the case statement to evaluate totrue. The when clause can be any expression that returns a Booleanvalue.