C＃空传播运营商/条件访问表达式和放大器;如果块 [英] C# Null propagating operator / Conditional access expression & if blocks

问题描述

借助空传播运营商/条件接收表达中的标签'C＃-6.0'的rel =标签> -6.0级=标签后称号=节目的问题看起来像一个非常方便的功能。不过我很好奇，如果这将有助于解决检查，如果一个子成员不为空，然后调用的布尔方法的问题上表示，内部的子成员如果块：

The Null propagating operator / Conditional access expression coming in c#-6.0 looks like quite a handy feature. But I'm curious if it will help solve the problem of checking if a child member is not null and then calling a Boolean method on said child member inside an if block:

  public class Container<int>{
       IEnumerable<int> Objects {get;set;}
  }

  public Container BuildContainer()
  { 
      var c = new Container();

      if (/* Some Random Condition */)
         c.Objects = new List<int>{1,2,4};
  }

  public void Test()
  {
      var c = BuildContainer();

      //Old way
      if ( null != c && null != c.Objects && c.Objects.Any())
         Console.Write("Container has items!");


      //C# 6 way?
      if (c?.Object?.Any())
          Console.Write("Container has items!");
  }

威尔 C吗？.Object？。任何（） 编译？如果经营者传播短路（我认为这是正确的术语）为空值，那么你必须如果（空），这是无效的。

Will c?.Object?.Any() compile? If the propagating operator short circuits (I assume that's the right term) to null then you have if (null), which isn't valid.

请问C＃团队解决这个问题还是我缺少空传播经营者预期使用情况？

Will the C# team address this concern or am I missing the intended use case for the null propagating operator?

推荐答案

它不会以这种方式工作。你可以跳过的解释，看看下面的代码：）

It won't work this way. You can just skip the explanation and see the code below :)

正如你所知道 运算符将返回null？如果一个子成员为空。但是，如果我们试图得到一个非空的成员，如任何（）方法，返回布尔会发生什么？答案是，编译器将包装一回在可空LT值&;> 。例如，对象？。任何（）会给我们布尔？（这是可空< ;布尔> ），而不是布尔

As you know ?. operator will return null if a child member is null. But what happens if we try to get a non-nullable member, like the Any() method, that returns bool? The answer is that the compiler will "wrap" a return value in Nullable<>. For example, Object?.Any() will give us bool? (which is Nullable<bool>), not bool.

这的确不是唯一的东西。让我们使用if 在这个表达式语句是它不能隐式强制转换为布尔。但你可以做的比较明确的，我喜欢比较真正是这样的：

The only thing that doesn't let us use this expression in the if statement is that it can't be implicitly casted to bool. But you can do comparison explicitly, I prefer comparing to true like this:

if (c?.Object?.Any() == true)
    Console.Write("Container has items!");

的感谢@DaveSexton 有另一种方式：

if (c?.Object?.Any() ?? false)
    Console.Write("Container has items!");

至于我，比较真正似乎更自然：）

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