c# - 为什么 ForEach 方法只适用于列表

Question

据我所知，ForEach 方法仅适用于 List class .

这是为什么呢？我看不出有什么理由让 ForEach 对任何实现 IEnumerable/IEnumerator 接口(interface)的类不可用，这是一个非常有用的方法，如果您需要执行一个小操作(1 行比 1 行 + 2 个样板 foreach 语法更具可读性...)。

更新:我会澄清我的问题。在序列中包含 ForEach 有完全正当的理由。有充分的理由不在所有序列中包含ForEach。

但我不明白为什么 ForEach 只包含在一些序列中。

Answer 1

请参阅 Eric Lippert 的帖子:"foreach" vs "ForEach"

A number of people have asked me why there is no Microsoft-provided “ForEach” sequence operator extension method. The List class has such a method already of course, but there’s no reason why such a method could not be created as an extension method for all sequences.

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But we can go a bit deeper here. I am philosophically opposed to providing such a method, for two reasons.

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The first reason is that doing so violates the functional programming principles that all the other sequence operators are based upon. Clearly the sole purpose of a call to this method is to cause side effects.

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The second reason is that doing so adds zero new representational power to the language.

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Well, the VS Languages team does not have any influence on what goes into List. I personally find the "ForEach" method on List philosophically troubling for all the same reasons that I would find an extension method on IEnumerable troubling. (And the VSL team does control that.) The one mitigating factor is that List is clearly designed to be a mutable, not-side-effect-free data structure, so using expressions that mutate it seems slightly less bad. -- Eric