“奇怪"的 C# 属性语法 [英] “Strange” C# property syntax

问题描述

我刚刚在一个 c# 项目中看到了这个:

I just saw this in a c# project:

public char this[int index]

我认为自己是 C# 的新手；任何人都可以帮助它是什么意思?

I consider myself new to C#; any one can help what it's meaning?

推荐答案

It is an Indexer.

It is an Indexer.

索引器允许类或结构的实例被索引，就像数组.索引器类似于属性，只是它们的访问器采用参数.索引器提供类似数组的语法.它允许访问类型与数组相同的方式.索引器等属性经常访问后备店.我们经常接受一个 int 类型的参数并访问一个数组类型的后备存储.

Indexers allow instances of a class or struct to be indexed just like arrays. Indexers resemble properties except that their accessors take parameters. An indexer provides array-like syntax. It allows a type to be accessed the same way as an array. Properties such as indexers often access a backing store. We often accept a parameter of int type and access a backing store of array type.

从 http://www.dotnetperls.com/indexer

string s = "hello";
Console.WriteLine (s[0]); // 'h'
Console.WriteLine (s[3]); // 'l'

实现索引器

要编写索引器，请定义一个名为 this 的属性，以正方形指定参数括号.例如:

To write an indexer, define a property called this, specifying the arguments in square brackets. For instance:

class Sentence
{
   string[] words = "The quick brown fox".Split();
   public string this [int wordNum] // indexer
   {
      get { return words [wordNum]; }
      set { words [wordNum] = value; }
   }
}

以下是我们如何使用此索引器:

Here’s how we could use this indexer:

Sentence s = new Sentence();
Console.WriteLine (s[3]); // fox
s[3] = "kangaroo";
Console.WriteLine (s[3]); // kangaroo

一个类型可以声明多个索引器，每个索引器都有不同类型的参数.一个indexer 也可以接受多个参数:

A type may declare multiple indexers, each with parameters of different types. An indexer can also take more than one parameter:

public string this [int arg1, string arg2]
{
  get  { ... } set { ... }
}

索引器在内部编译为名为 get_Item 和 set_Item 的方法，如下所示:

Indexers internally compile to methods called get_Item and set_Item, as follows:

public string get_Item (int wordNum) {...}
public void set_Item (int wordNum, string value) {...}

编译器默认选择名称Item——你实际上可以通过使用以下属性装饰您的索引器:

The compiler chooses the name Item by default—you can actually change this by decorating your indexer with the following attribute:

[System.Runtime.CompilerServices.IndexerName ("Blah")]

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