类型上有多个索引属性? [英] Multiple index properties on a type?

问题描述

在C#中是否可能有类似的东西?我不太确定:

Is it possible to have something like this in C#? I am not very sure:

class Library
{
    public string Books[string title]
    {
        get{return this.GetBookByName(string title);}
    }

    public DateTime PublishingDates[string title]
    {
        get{return this.GetBookByName(string title).PublishingDate;}
    }
}

因此可以这样使用:

myLibrary.Books["V For Vendetta"]
myLibrary.PublishingDates["V For Vendetta"] = ...

因此，我需要在我的框架中(通过调用它们)实现的完整成员方法是:

So my complete member methods that I need to implement in my framework (by calling them) are:

GetCustomStringValue (key)
GetCustomIntValue (key)
GetCustomBoolValue (key)
GetCustomFloatValue (key)
SetCustomStringValue (key)
SetCustomIntValue (key)
SetCustomBoolValue (key)
SetCustomFloatValue (key)

我想以自己的类型将它们实现得更干净.

I want to implement them cleaner in my own type.

推荐答案

唯一的方法是让 Books 是一个属性，该属性返回具有自己合适的索引器的类型.这是一种可能的方法:

The only way you could do this would be to have Books be a property that returns a type that has its own suitable indexer. Here's one possible approach:

public class Indexer<TKey, TValue>
{
    private Func<TKey, TValue> func;

    public Indexer(Func<TKey, TValue> func)
    {
        if (func == null)
            throw new ArgumentNullException("func");

        this.func = func;
    }

    public TValue this[TKey key]
    {
        get { return func(key); }
    }
}

class Library
{
    public Indexer<string, Book> Books { get; private set; }
    public Indexer<string, DateTime> PublishingDates { get; private set; }

    public Library()
    {
        Books = new Indexer<string, Book>(GetBookByName);
        PublishingDates = new Indexer<string, DateTime>(GetPublishingDate);
    }

    private Book GetBookByName(string bookName)
    {
        // ...
    }

    private DateTime GetPublishingDate(string bookName)
    {
        return GetBookByName(bookName).PublishingDate;
    }
}

但是您应该认真考虑提供 IDictionary<> 的实现，而不是使用这种方法，因为它会允许其他一些漂亮的东西，例如键值对的枚举等.

But you should seriously consider providing an implementation of IDictionary<,> instead of using this approach, as it will allow other nifty stuff, like enumeration of key-value pairs, etc.

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