C＃中的三元运算符关联性-我可以依靠它吗？ [英] Ternary operator associativity in C# - can I rely on it?

问题描述

啊，你不只是爱好三元虐待吗？ :)考虑以下表达式：

Ahh, don't you just love a good ternary abuse? :) Consider the following expression:

true ? true : true ? false : false

对于现在完全困惑的那些人，我可以告诉你，这等于是。换句话说，它等于：

For those of you who are now utterly perplexed, I can tell you that this evaluates to true. In other words, it's equivalent to this:

true ? true : (true ? false : false)

但这可靠吗？我可以确定在某些情况下不会出现这种情况吗？

But is this reliable? Can I be certain that under some circumstances it won't come to this:

(true ? true : true) ? false : false

有人可能会说-好吧，那就加括号然后不使用总共-毕竟，众所周知，三元运算符是邪恶的！

当然可以，但是在某些情况下它们确实有意义。对于那些好奇的人-我正在拧代码，按照一系列属性比较两个对象。如果我像这样冷写它，那就太好了：

Sure they are, but there are some circumstances when they actually make sense. For the curious ones - I'm wring code that compares two objects by a series of properties. It would be pretty nice if I cold write it like this:

obj1.Prop1 != obj2.Prop1 ? obj1.Prop1.CompareTo(obj2.Prop1) :
obj1.Prop2 != obj2.Prop2 ? obj1.Prop2.CompareTo(obj2.Prop2) :
obj1.Prop3 != obj2.Prop3 ? obj1.Prop3.CompareTo(obj2.Prop3) :
obj1.Prop4.CompareTo(obj2.Prop4)

简洁明了。但这确实取决于像在第一种情况下那样的三元算子关联性。括号只会使它成为意大利面条。

Clear and concise. But it does depend on the ternary operator associativity working like in the first case. Parenthesis would just make spaghetti out of it.

所以-是否在任何地方都指定了？我找不到它。

So - is this specified anywhere? I couldn't find it.

推荐答案

是的，您可以依靠它（不仅在C＃中，而且在所有方面（我知道）带有条件运算符的其他语言（ PHP …除外） ），而您的用例实际上是一种很常见的做法，尽管有人对此表示反对。

Yes, you can rely on this (not only in C# but in all (that I know) other languages (except PHP … go figure) with a conditional operator) and your use-case is actually a pretty common practice although some people abhor it.

ECMA-334（C＃标准）的相关部分为14.13§3：

The relevant section in ECMA-334 (the C# standard) is 14.13 §3:

条件运算符是右关联的，这意味着运算从右到左分组。
[示例： a形式的表达式？ b：c？ d：e 被评估为 a？ b：（c？d：e）。结束
示例]

The conditional operator is right-associative, meaning that operations are grouped from right to left. [Example: An expression of the form a ? b : c ? d : e is evaluated as a ? b : (c ? d : e). end example]

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