问题标签 [null-conditional-operator]

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72 问题

0 投票

4 回答

214 浏览

c# - ?. C# 中的运算符由于未知原因未编译

在以下代码中，两个变体之一无法编译：

错误 CS0023：操作员“？” 不能应用于“十进制”类型的操作数

为什么简单表单无法编译？

表达式c?.DecimalField不会是 typedecimal?吗？该值可以为 null，因此?.应应用运算符。我很确定这是因为在这段代码中：

var确实根据decimal?IDE解析。

c#.net c#-6.0 null-conditional-operator

0 投票

2 回答

438 浏览

c# - 当 null 条件运算符短路时，它是否仍然评估方法参数？

null 条件运算符可用于跳过对 null 目标的方法调用。在这种情况下是否会评估方法参数？

例如：

什么GetFromNetwork时候myObject叫null？

c#c#-6.0 null-conditional-operator

0 投票

1 回答

8837 浏览

c# - 使用空条件布尔？在 if 语句中

为什么此代码有效：

但这段代码没有：

说错误 CS0266 无法隐式转换类型“bool？” '布尔'

那么为什么在if语句中进行这种隐式转换不是语言特性呢？

c#c#-6.0 null-conditional-operator

0 投票

3 回答

2317 浏览

c# - Using the Null Conditional Operator to check values on objects which might be null

I've been playing with C# 6's Null Conditional Operator (more info here).

I really like the syntax and I think it makes the code much more readable however I think it is questionable as to what exactly the code is going to do when you come across checking the value of a property on an object which itself might be null.

For example, if I had a class with a decimal property on it and I wanted a conditional check on the value of that decimal, I would write something like:

On the surface this looks great... If foo is not null, get the value of Bar and check if it's greater than a maximum value, if it is, do something.

However, what if foo is null?!

This documentation about the new and improved features of C# 6 says something along these lines:

if in fact the value of the object is null, the null-conditional operator will return null. It short-circuits the call to Bar, and immediately returns null, avoiding the programming error that would otherwise result in a NullReferenceException.

I've written a fiddle here which shows that it does indeed work and is doing what I'm expecting it to do however I can't get my head around how it is deciding the result of the condition.

How does the short-circuit equal a false? In my head this code is now going to say "If foo is null, check if null is > max, which is impossible, so return false" or "If foo is null, then foo != null will return false, so you get a false" however the documentation says the null conditional check returns null, not false.

c#c#-6.0 null-conditional-operator

0 投票

1 回答

296 浏览