C# 使用 Foreach 子句的 Lambda 表达式

Lambda Expression using Foreach Clause

提问by Eoin Campbell

Possible Duplicate:
Why is there not a ForEach extension method on the IEnumerable interface?

可能的重复：
为什么 IEnumerable 接口上没有 ForEach 扩展方法？

EDIT

编辑

For reference, here's the blog post which eric referrrred to in the comments

作为参考，这是 eric 在评论中引用的博客文章

http://blogs.msdn.com/ericlippert/archive/2009/05/18/foreach-vs-foreach.aspx

http://blogs.msdn.com/ericlippert/archive/2009/05/18/foreach-vs-foreach.aspx

ORIG

原点

More of a curiosity I suppose but one for the C# Specification Savants...

我想更多的是好奇心，但对 C# 规范学者来说是一种好奇心......

Why is it that the ForEach() clause doesn't work (or isn't available) for use on IQueryable/IEnumerable result sets...

为什么 ForEach() 子句在 IQueryable/IEnumerable 结果集上不起作用（或不可用）...

You have to first convert your results ToList() or ToArray() Presumably theres a technical limitation to the way C# iterates IEnumerables Vs. Lists... Is it something to do with the Deferred Execution's of IEnumerables/IQuerable Collections. e.g.

您必须首先将结果转换为 ToList() 或 ToArray() 大概有 C# 迭代 IEnumerables 的方式的技术限制。列表...是否与 IEnumerables/IQuerable 集合的延迟执行有关。例如

var userAgentStrings = uasdc.UserAgentStrings
    .Where<UserAgentString>(p => p.DeviceID == 0 && 
                            !p.UserAgentString1.Contains("msie"));
//WORKS            
userAgentStrings.ToList().ForEach(uas => ProcessUserAgentString(uas));         

//WORKS
Array.ForEach(userAgentStrings.ToArray(), uas => ProcessUserAgentString(uas));

//Doesn't WORK
userAgentStrings.ForEach(uas => ProcessUserAgentString(uas));

采纳答案by Eric Lippert

What an amazing coincidence, I just now wrote a blog article about this very question. It will bewas published May 18th. There is no technical reason why we (or you!) couldn't do this. The reasons why not are philosophical. See my blog next week for my argument.

多么惊人的巧合，我刚刚写了一篇关于这个问题的博客文章。这将公布5月18日。我们（或您！）无法做到这一点没有任何技术原因。原因是哲学上的。我的论点下周见我的博客。

回答by LukeH

It's perfectly possible to write a ForEachextension method for IEnumerable<T>.

完全可以ForEach为IEnumerable<T>.

I'm not really sure why it isn't included as a built-in extension method:

我不确定为什么它不作为内置扩展方法包含在内：

• Maybe because ForEachalready existed on List<T>and Arrayprior to LINQ.
• Maybe because it's easy enough to use a foreachloop to iterate the sequence.
• Maybe because it wasn't felt to be functional/LINQy enough.
• Maybe because it isn't chainable. (It's easy enough to make a chainable version that yields each item after performing an action, but that behaviour isn't particularly intuitive.)

• 也许是因为ForEach已经存在的List<T>和Array之前LINQ。
• 也许是因为使用foreach循环来迭代序列很容易。
• 也许是因为感觉功能/LINQ 不够。
• 也许是因为它不可链接。（yield在执行操作后制作每个项目的可链接版本很容易，但这种行为并不是特别直观。）

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public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
    if (source == null) throw new ArgumentNullException("source");
    if (action == null) throw new ArgumentNullException("action");

    foreach (T item in source)
    {
        action(item);
    }
}