如何OfType＆LT; T＆GT;（）的工作？ [英] How does OfType<T>() Work?

问题描述

如何OfType（）的工作？

How does OfType() Work?

我看了这是怎么回事上，但究竟怎样的LINQ提供此链接知道如何匹配指定类型的所有对象。我知道的IQueryable＆LT; T＆GT; 链上的请求，然后评估时的GetEnumerator（）被称为（右？ ）。

I read this link about what's going on but how exactly does the LINQ provider know how to get all objects matching the specified type. I know the IQueryable<T> "chains" up requests and then evaluates when GetEnumerator() is called (right?).

具体来说，我想知道如何框架快快行动类型的比较？我在.NET 2.0的项目，去这样的（因为2.0不支持这些类型的功能）写了一个方法：

Specifically I want to know how does the framework quickly do type comparison? I wrote a method in a .NET 2.0 project that went like this (since 2.0 doesn't support these kind of features):

    public IEnumerable<TResult> OfType<TResult>()
        where TResult : class
    {
        foreach (TItem item in this.InnerList)
        {
            TResult matchItem = item as TResult;

            if (matchItem != null)
            {
                yield return matchItem;
            }
        }
    }

这是最好的实现？

编辑：我主要关注本 OfType＆LT; T＆GT;（）是它的快速的

My main concern with this OfType<T>() is that it is fast.

推荐答案

您目前的实现 - 设计 - 不支持值类型

Your current implementation -- by design -- doesn't support value-types.

如果你想更接近于LINQ的 OfType 的方法，支持所有类型的，那么试试这个：

If you wanted something closer to LINQ's OfType method, that supports all types, then try this:

public IEnumerable<TResult> OfType<TResult>(IEnumerable source)
{
    foreach (object item in source)
    {
        if (item is TResult)
            yield return (TResult)item;
    }
}

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