命名在C＃中的索引属性？ [英] Named indexed property in C#?

问题描述

几种语言 - 像德尔福 - 具有创建索引的一个非常方便的方法：不仅全班，但即使是单一的属性可以被索引，比如：

A few languages - like Delphi - has a very convenient way of creating indexers: not only the whole class, but even single properties can be indexed, for instance:

type TMyClass = class(TObject)
protected
    function GetMyProp(index : integer) : string;
    procedure SetMyProp(index : integer; value : string);
public
    property MyProp[index : integer] : string read GetMyProp write SetMyProp;
end;

这可以很容易地使用：

var c : TMyClass;

begin
    c = TMyClass.Create;
    c.MyProp[5] := 'Ala ma kota';
    c.Free;
end;

有没有办法实现在C＃中容易吗？

Is there a way to achieve the same effect in C# easily?

推荐答案

众所周知的解决方案是创建一个代理类：

The well-known solution is to create a proxy class:

public class MyClass
{
    public class MyPropProxy
    {
        private MyClass c;

        // ctor etc.

        public string this[int index]
        {
            get
            {
                return c.list[index];
            }
            set
            {
                c.list[index] = value;
            }
        }
    }

    private List<string> list;
    private MyPropProxy myPropProxy;

    // ctor etc.

    public MyPropProxy MyProp
    { 
        get
        {
            return myPropProxy;
        }
    }
}

但（有例外，那这实际上解决了这个问题），这种解决方案大多只能缺点：

But (with exception, that this actually solves the problem), this solution introduces mostly only cons:

• 这导致代码以通过（可能）有很多被污染小代理类。


• 主办解决方案打破了封装的一点点的（内部类访问外部类的私有成员），一个更好的将通过列表的实例 MyPropProxy 构造函数，你会需要更多的代码。


• 揭露内部辅助类是不是我会建议。有人可能会解决通过引入额外的接口，但是这甚至多一个实体来实现（测试，维护等）

• It causes the code to be polluted by (possibly) a lot of small proxy classes.
• Presented solution breaks encapsulation a little (inner class accesses private members of the outer class), a better one would pass an instance of list to MyPropProxy's ctor, what would require even more code.
• Exposing internal helper classes is not something I would suggest. One may solve that by introducing additional interface, but that's even one more entity to implement (test, maintain etc.)

有另一种方法，虽然。它也污染了代码一点，但肯定少了很多，比前一个：

There's another way, though. It also pollutes the code a little, but surely a lot less, than the previous one:

public interface IMyProp
{
    string this[int index] { get; }
}

public class MyClass : IMyProp
{
    private List<string> list;

    string IMyProp.this[int index]
    {
        get
        {
            return list[index];
        }
        set
        {
            list[index] = value;
        }
    }

    // ctor etc.

    public IMyProp MyProp 
    {
        get
        {
            return this;
        }
    }
}

优点：

Pros:

• 无代理类（占用的内存空间，服务只有一个目的，（最简单的解决方案）打破封装。


• 简单的解决方案，只需要很少的代码添加其他索引属性

缺点：

• 每个属性需要不同的公共接口


• 随着索引属性的增加，类实现更多接口

这是最简单的（代码长度和复杂性方面）引入索引属性到C＃的方式。除非有人张贴更短和更简单的之一，当然。

This is the simplest (in terms of code length and complexity) way of introducing indexed properties to C#. Unless someone posts even shorter and simpler one, of course.

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