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C# 9 中进一步增强了模式匹配的用法,使得模式匹配更为强大,我们一起来了解一下吧
C# 9 中增强了模式匹配的用法,增加了 and
/or
/not
操作符,而且可以直接判断属性,来看一下下面的这个示例:
var person = new Person();// or// string.IsNullOrEmpty(person.Description)if (person.Description is null or { Length: 0 }){ Console.WriteLine($"{nameof(person.Description)} is IsNullOrEmpty");}// and// !string.IsNullOrEmpty(person.Name)if (person.Name is not null and { Length: > 0 }){ if (person.Name[0] is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z') or '.') { }}// notif (person.Name is not null){}
这里的代码使用 DnSpy
反编译之后的代码是下面这样的:
Person person = new Person();string text = person.Description;bool flag = text == null || text.Length == 0;if (flag){ Console.WriteLine("Description is IsNullOrEmpty");}text = person.Name;bool flag2 = text != null && text.Length > 0;if (flag2){ char c = person.Name[0]; if (c >= 'a') { if (c > 'z') { goto IL_8B; } } else if (c >= 'A') { if (c > 'Z') { goto IL_8B; } } else if (c != ',' && c != '.') { goto IL_8B; } bool flag3 = true; goto IL_8E; IL_8B: flag3 = false; IL_8E: bool flag4 = flag3; if (flag4) { }}bool flag5 = person.Name != null;if (flag5){}
这不仅适用于 is
也可以在 switch
中使用
switch (person.Age){ case >= 0 and <= 3: Console.WriteLine("baby"); break; case > 3 and < 14: Console.WriteLine("child"); break; case > 14 and < 22: Console.WriteLine("youth"); break; case > 22 and < 60: Console.WriteLine("Adult"); break; case >= 60 and <= 500: Console.WriteLine("Old man"); break; case > 500: Console.WriteLine("monster"); break;}
反编译后的代码:
int age = person.Age;int num = age;if (num < 22){ if (num < 14) { if (num >= 0) { if (num > 3) { Console.WriteLine("child"); } else { Console.WriteLine("baby"); } } } else if (num > 14) { Console.WriteLine("youth"); }}else if (num < 60){ if (num > 22) { Console.WriteLine("Adult"); }}else if (num > 500){ Console.WriteLine("monster");}else{ Console.WriteLine("Old man");}
可以看到有些情况下可以简化不少代码,尤其是 if
分支比较多的情况下使用上面 switch
这样的写法会清晰很多
但是如果只是 string.IsNullOrEmpty
这种代码最好还是不要写得这么骚了,小心要被同事吐槽了
炫技需谨慎,小心被 ...
https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-9
https://github.com/WeihanLi/SamplesInPractice/tree/master/CSharp9Sample
https://github.com/WeihanLi/SamplesInPractice/blob/master/CSharp9Sample/PatternMatchingSample.cs
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