C#8中的范围和索引类型是什么? [英] What are Range and Index types in C# 8?

问题描述

在C#8中，向系统名称空间添加了两种新类型: System.Index 和 System.Range .

In C# 8, two new types are added to the System namespace: System.Index and System.Range.

它们如何工作，什么时候可以使用它们?

How do they work and when can we use them?

推荐答案

它们用于索引和切片.来自微软的博客:

They're used for indexing and slicing. From Microsoft's blog:

索引:

Index i1 = 3;  // number 3 from beginning
Index i2 = ^4; // number 4 from end
int[] a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
Console.WriteLine($"{a[i1]}, {a[i2]}"); // "3, 6"

范围(切片)

我们还引入了范围类型，它由两个索引组成，一个用于开始，一个用于结束，并且可以用x..y编写范围表达式.然后，您可以使用Range进行索引以产生一片:

We’re also introducing a Range type, which consists of two Indexes, one for the start and one for the end, and can be written with a x..y range expression. You can then index with a Range in order to produce a slice:

var slice = a[i1..i2]; // { 3, 4, 5 }

您可以在 Array ， String ， [ReadOnly] Span 和 [ReadOnly] Memory 类型中使用它们，因此您还有另一种制作子字符串的方法:

You can use them in Array, String, [ReadOnly]Span and [ReadOnly]Memory types, so you have another way to make substrings:

string input = "This a test of Ranges!";
string output = input[^7..^1];
Console.WriteLine(output); //Output: Ranges

您还可以省略范围的第一个或最后一个索引:

You can also omit the first or last Index of a Range:

output = input[^7..]; //Equivalent of input[^7..^0]
Console.WriteLine(output); //Output: Ranges!

output = input[..^1]; //Equivalent of input[0..^1]
Console.WriteLine(output); //Output: This a test of Ranges

您还可以将范围保存到变量中，并在以后使用它们:

You can also save ranges to variables and use them later:

Range r = 0..^1;
output = input[r];
Console.WriteLine(output);

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