数字和为空的数字之间加/减的有悖常理的设计 [英] Counterintuitive design of addition/subtraction between numbers and nullable numbers

问题描述

让我们来看看下面的代码：

Let's see the following code:

int a = 1;
int? b = null;
var addition = a + b;
var subtraction = a - b;

我希望这两个除了和减法是 1 。但事实上这两个两个是空。没有语法糖生成的代码是这样的：

I expect both addition and subtraction is 1. But in fact both of the two are null. The generated code without syntax sugars is like this:

int? addition = b.HasValue ? new int?(a + b.GetValueOrDefault()) : new int?();

从VB.NET的观点，这是违反直觉的更多：的THRE结果1 +没什么是没有。

我认为他们能做到这增加轻松的方式：

I think they could do the addition in this way easily:

int addition = a + b.GetValueOrDefault();
//or int? addition = a + b.GetValueOrDefault();

不过说实话，目前的设计不破的其关联。我的问题是：为什么他们设计这样的操作？什么是我的预期行为的缺点？

But to be honest, the current design doesn't break its associativity. My question is: why do they design the operator like this? What is the disadvantage of my expected behavior?

修改几点意见提到，因为空不是 0 ，这是绝对正确的。但是，这并不是说 1 +空== NULL ，我没有说空是<$ C $的原因C> 0 。为什么不能 1 +空== 1 ？需要注意的是：即使 1 +空== 1 和 1 + 0 == 1 ，也不能推断空== 0 。如果是这样， 1 +空== NULL 和 2 +空== NULL ，我也可以推断出 1 == 2 ，这是没有意义的。在空是由编译器团队，为什么他们选择这条规则，增加空为int和字符串之间的不同定义的操作规则。

EDIT A few comments mentioned that "because null is not 0", this is absolutely correct. But it's not the reason that 1+null==null, I didn't say null is 0. Why can't 1+null==1? Note that: even 1+null==1 and 1+0==1, we can't infer null==0. If so, 1+null==null and 2+null==null, I can also infer 1==2, which makes no sense. Operation rules on null is defined by the compiler team, why do they choose this rule, different between adding null to int and string.

修改考虑空是我不知道，那么你怎么解释，加入空为字符串1，使原来的1，而不是空的（我不知道）？记住空不是的String.Empty ！

EDIT consider null as "i have no idea", then how did you explain that adding null to a string "1" gives the original "1" instead of null(i have no idea)? Remember null is not string.Empty!

< STRONG>修改我不相信没有数学的担忧在这里，因为在一些语言 1 +空收益 1 （试行的JavaScript）。所以它只是一个（也许个人）的选择，由语言设计者（S）。 IMO 1 +空== 1 更容易比目前的设计中使用。这可能是一个初级的意见基础的问题。

EDIT I do believe there is no mathematics concerns here, because in some languages 1 + null returns 1 (try javascript). So it's just a (maybe personal) choice, by the language designer(s). IMO 1 + null == 1 is easier to use than the current design. It's probably a primary-opinion based question.

推荐答案

如果 1 +空== 1 ，然后再考虑以下内容：

If 1 + null == 1, then consider the following:

int a = 1;
int? b = null;
int result = a + b;
int difference = (a + b) - a;

bool zeroEqualsNull = (difference == b);

结果将是 INT ，而不是 INT？，因为我们知道 INT +空== INT

result would be an int, not an int? as we know int + null == int

显然，区别可重新安排简单地 b 。然后，我们比较 B == b ，其中应的给予真正。

Clearly, difference can be re-arranged to simply b. We're then comparing b == b, which should give true.

然而 B 是空，而不是 0 。如果 0 == NULL 我们会在一个可怕的局面。为什么甚至使用 INT？在所有在这种情况下？

Yet b is null, not 0. And if 0 == null we'd in a terrible situation. Why even use int? at all in that case?

当然，除非，区别竟然是 INT - 这意味着无论是加法或减法操作必须在某些情况下，返回空。

Unless, of course, difference turned out to be int? - which means either the addition or subtraction operation must, in some cases, return null.

PS指向JavaScript作为一种语言应该表现如何是一个坏主意的引用;）

P.S. Pointing to javascript as a reference for how a language should behave is a bad idea ;)

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