发送一个序列LINQ项目返回void的方法 [英] Sending items in a LINQ sequence to a method that returns void

问题描述

通常情况下，而我处理LINQ序列，我想每一个项目发送到返回void的方法，避免foreach循环。但是，我还没有找到一个优雅的方式来做到这一点。今天，我写了下面的代码：

Often while I'm dealing with LINQ sequences, I want to send each item to a method returning void, avoiding a foreach loop. However, I haven't found an elegant way to do this. Today, I wrote the following code:

    private StreamWriter _sw;
    private void streamToFile(List<ErrorEntry> errors)
    {
        if (_sw == null)
        {
            _sw = new StreamWriter(Path.Combine
                                    (Path.GetDirectoryName(_targetDatabasePath), "errors.txt"));
        }

        Func<ErrorEntry, bool> writeSelector = 
            (e) => { _sw.WriteLine(getTabDelimititedLine(e)); return true; };

        errors.Select(writeSelector);

        _sw.Flush();
    }

正如你所看到的，我写的lambda函数，仅仅返回true，并我认识到，选择的方法会返回booleans-我就忽略该序列的序列。然而，这似乎有点noobish和JANK。是否有任何优雅的方式来做到这一点？还是我误用LINQ？

As you can see, I write a lambda function that just returns true, and I realize that the Select method will return a sequence of booleans- I'll just ignore that sequence. However, this seems a little bit noobish and jank. Is there any elegant way to do this? Or am I just misapplying LINQ?

感谢。

推荐答案

第一所有的，你当前的代码将无法正常工作。结果
选择，和其他大多数LINQ的方法，使用延迟执行，这意味着它们实际上没有做任何事情，直到你列举的结果。

First of all, your current code will not work.
Select, and most other LINQ methods, use deferred execution, meaning that they don't actually do anything until you enumerate the results.

在一般情况下，你不应该使用带有副作用LINQ查询的lambda。

In general, you should never use a lambda with side effects in a LINQ query.

要回答你的问题，你应该使用的foreach 循环。

To answer your question, you should use a foreach loop.

您正在寻找一个的ForEach 扩展方法; 埃里克利珀解释了为什么微软没有写一个。

You're looking for a ForEach extension method; Eric Lippert explains why Microsoft didn't write one.

如果你真的想，你可以写一个自己的：

If you really want to, you can write one yourself:

public static void ForEach<T>(this IEnumerable<T> sequence, Action<T> action) {
    if (sequence == null) throw new ArgumentNullException("sequence");
    if (action == null) throw new ArgumentNullException("action");
    foreach(T item in sequence) 
        action(item);
}

//Return false to stop the loop
public static void ForEach<T>(this IEnumerable<T> sequence, Func<T, bool> action) {
    if (sequence == null) throw new ArgumentNullException("sequence");
    if (action == null) throw new ArgumentNullException("action");

    foreach(T item in sequence) 
        if (!action(item))
            return;
}

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