可能重复：   Why是不是有IEnumerable接口上一个foreach扩展方法？

您好，

我的问题是，为什么的Foreach扩展方法是对列表，而不是IEnumreable定义。我已阅读埃里克利珀的文章但问题是，如果是如此糟糕，有这样的方法比为什么会在那里列表？

My question is why Foreach extension method is defined on List rather than IEnumreable. i have read Eric Lippert's article but the point is, if it is so bad to have such method than why is it there for List?

推荐答案

名单，其中，T＆GT; .ForEach（）不是一个扩展方法。这只是对列表℃的方法; T＆GT;

List<T>.ForEach() isn't an extension method. It's just a method on List<T>.

其中一个主要的原因，这是不具备的LINQ（即可枚举）是LINQ查询应该是免费的副作用（所以你可以，例如，执行一个查询多次，得到相同的结果不会更改），这让他们很可组合。所有的LINQ操作接受委托对 Func键;他们没有接受动作委托。

One of the main reasons that it isn't available in LINQ (i.e., Enumerable) is that LINQ queries are supposed to be free of side-effects (so you can, e.g., execute a query multiple times and get the same results without changing them), which makes them very composable. All the LINQ operations that accept delegates are for Func; none of them accept an Action delegate.