为什么是IList的＆LT .ForEach（）; T＆GT;而不是IEnumerable的＆LT; T＆GT ;? [英] Why is .ForEach() on IList<T> and not on IEnumerable<T>?

问题描述

可能重复：结果
  <一href=\"http://stackoverflow.com/questions/101265/why-is-there-not-a-foreach-extension-method-on-the-ienumerable-interface\">Why是不是有IEnumerable接口上一个foreach扩展方法？

我写LINQ-Y code，它.ForEach（）是一个很好的成语使用时注意。例如，这里是一片code的，它采用以下输入，并产生这些输出：

I've noticed when writing LINQ-y code that .ForEach() is a nice idiom to use. For example, here is a piece of code that takes the following inputs, and produces these outputs:

{ "One" } => "One"
{ "One", "Two" } => "One, Two"
{ "One", "Two", "Three", "Four" } => "One, Two, Three and Four";

而code：

private string InsertCommasAttempt(IEnumerable<string> words)
{
    List<string> wordList = words.ToList();
    StringBuilder sb = new StringBuilder();
    var wordsAndSeparators = wordList.Select((string word, int pos) =>
        {
            if (pos == 0) return new { Word = word, Leading = string.Empty };
            if (pos == wordList.Count - 1) return new { Word = word, Leading = " and " };
            return new { Word = word, Leading = ", " };
        });

    wordsAndSeparators.ToList().ForEach(v => sb.Append(v.Leading).Append(v.Word));
    return sb.ToString();
}

请注意在.ForEach面前的第二个插话.ToList（）（）到最后一行。

Note the interjected .ToList() before the .ForEach() on the second to last line.

为什么说.ForEach（）不能作为对IEnumerable的扩展方法？有了这样的一个例子，它只是似乎不可思议。

Why is it that .ForEach() isn't available as an extension method on IEnumerable? With an example like this, it just seems weird.

由于提前，

戴夫

推荐答案

由于<一个href=\"http://msdn.microsoft.com/en-us/library/bwabdf9z%28VS.80%29.aspx\"><$c$c>ForEach(Action)前存在的IEnumerable＆LT; T＆GT; 存在

既然不与其他扩展方法添加，你可以假设C＃的设计师认为这是一个不好的设计和preFER的的foreach 结构。

Since it was not added with the other extension methods, one can assume that the C# designers felt it was a bad design and prefer the foreach construct.

---

如果你愿意，你可以创建自己的扩展方法，它不会覆盖一个用于列表＆LT; T＆GT; ，但它会为任何其他类，它实现工作的IEnumerable＆LT; T＆GT;

If you want you can create your own extension method, it won't override the one for a List<T> but it will work for any other class which implements IEnumerable<T>.

public static class IEnumerableExtensions
{
  public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
  {
    foreach (T item in source)
      action(item);
  }
}

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