多重枚举和使用Any() [英] Multiple enumeration and use of Any()

问题描述

当我需要执行以下操作时，我试图弄清楚LINQ的正确约定是什么

I'm trying to figure out what would be the proper convention for LINQ when I need to do something like the following

• 如果有项目，请逐行打印它们
• 如果没有项目，请打印没有项目"

我想去做的方式就像

if (items.Any())
{
    foreach (string item in items)
    {
        Console.WriteLine(item);
    }
}
else
{
    Console.WriteLine("No items");
}

但是，从技术上讲，这将违反多重枚举的原理.一种不违反规定的方法是

However, that would technically violate the principle of multiple enumeration. A way to not violate that would be

bool any = false;
foreach (string item in items)
{
    any = true;
    Console.WriteLine(item);
}   
if (!any)
{
    Console.WriteLine("No items");
}

但很明显，这不太优雅.

but clearly, that is less elegant.

推荐答案

既然我们在谈论LINQ，那么一个非常LINQ的解决方案又如何呢?

Since we are talking LINQ, how about a very LINQ solution?

foreach (var item in items.DefaultIfEmpty("No items"))
    Console.WriteLine(item);

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