从List< X>转换的较短语法到列表< Y&gt ;? [英] Shorter syntax for casting from a List<X> to a List<Y>?

问题描述

我知道可以一次将一种类型的项目列表转换为另一种类型(假设您的对象具有公共静态显式运算符方法进行转换)，如下所示:

I know its possible to cast a list of items from one type to another (given that your object has a public static explicit operator method to do the casting) one at a time as follows:

List<Y> ListOfY = new List<Y>();

foreach(X x in ListOfX)
    ListOfY.Add((Y)x);

但是不可能一次转换整个列表吗?例如，

But is it not possible to cast the entire list at one time? For example,

ListOfY = (List<Y>)ListOfX;

推荐答案

如果真的可以将X强制转换为Y，则应该可以使用

If X can really be cast to Y you should be able to use

List<Y> listOfY = listOfX.Cast<Y>().ToList();

需要注意的一些事情(向评论者致敬！)

Some things to be aware of (H/T to commenters!)

• 您必须包含using System.Linq;才能获取此扩展方法
• 这将强制转换列表中的每个项目-而不是列表本身.调用ToList()将创建一个新的List<Y>.
• 此方法不支持自定义转换运算符. (请参见 http://stackoverflow.com/questions/14523530/为什么linq-cast-helper不能与隐式播放操作符一起工作)
• 此方法不适用于具有显式运算符方法(框架4.0)的对象

• You must include using System.Linq; to get this extension method
• This casts each item in the list - not the list itself. A new List<Y> will be created by the call to ToList().
• This method does not support custom conversion operators. ( see http://stackoverflow.com/questions/14523530/why-does-the-linq-cast-helper-not-work-with-the-implicit-cast-operator )
• This method does not work for an object that has a explicit operator method (framework 4.0)

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