如何在不返回值的情况下使用三元运算符? [英] How Do I Can Using Ternary Operator Without Return A Value?

问题描述

大家好，

我想像这样使用三元运算符，但是它不起作用.

Hello people,

I want use the ternary operator like this, but it doesn''t work.

var itemToRemove = myCollection.Any(p => p != null).FirstOrDefault();
itemToRemove != null ?? myCollection.Remove(itemToRemove); //this don't compile!

It''s Possible?

推荐答案

这里有两个问题:
1)Any返回一个bool，而不是一个集合，因此您不能在其上使用FirstOrDefault.
2)null-coalescing运算符不能那样工作.阅读MSDN描述:? OPerator [^ ]

我不太确定您认为该代码应达到的目标，所以我真的无法提出任何解决方案-也许如果您告诉我们您正在尝试做的事情可能会有所帮助?

There are a couple of problems here:
1) Any returns a bool, not a collection, so you can''t use FirstOrDefault on it.
2) The null-coalescing operator does not work like that. Read the MSDN description: ?? OPerator[^]

I''m not quite sure what the heck you think that code should achieve, so I can''t really suggest anything to fix it - perhaps if you told us what you were trying to do it might help?

进一步了解OriginalGriff的解决方案，

三元运算符也不能那样工作
http://www.dotnetperls.com/ternary [
遵循MCY的建议，并使用if

Further to OriginalGriff''s solution,

The Ternary Operator doesn''t work like that either
http://www.dotnetperls.com/ternary[^] - the clue is in the name "operator"

Follow the advice from MCY and use if

if( itemToRemove != null)
    myCollection.Remove(itemToRemove);

您的代码未使用三元运算符:您正在使用"??"计算一个参数(变量)的运算符，如果该值非空，则返回所计算的值；如果该值为空，则在"??"之后的值返回.示例:

Your code does not make use of the ternary operator: you are using the "??" operator which evaluates an argument (a variable), and if the value is non-null, returns the evaluated value; if the value is null, then the value after the "??" is returned. Example:

string s1 = null;

string t1 = s1 ?? "whoop de doo"; // t1 now contains "whoop de doo"

string s2 = "hoop la";

string t2 = s2 ?? "yabba dabba doo" // t2 now contains "hoop la"

您可以使用三元运算符，Microsoft将该三元运算符称为条件运算符"，该运算符必须始终 返回值:

You can use the ternary operator, referred to by Microsoft as the "conditional operator," which must always return a value:

string t3 = (s1 != null) ? t2 : "shake, rattle, and roll";
// t3 contains "shake, rattle, and roll"

，两者都包含???和三元运算符，您只能在每个段"中使用一个语句，并且必须返回某些内容.

显然，您的目标是从集合中删除一个项目.请记住，.NET Collections Remove< T>操作员返回一个布尔值，指示移除成功或失败；您可以使用该返回值，也可以忽略它.如果需要跟踪删除是否成功，请尝试以下操作:

With both ?? and ternary operators you are limited to one statement in each "segment," and you must return something.

Clearly, your goal here is to remove an item from a collection. Keep in mind that .NET Collections Remove<T> operator returns a boolean value indicating the success or failure of a removal; you can use that return value, or ignore it. If you need to keep track of whether the removal was successful, try this:

bool itemIsRemoved = myCollection.Remove(myCollection.FirstOrDefault(p => p != null));

这是一个挑战:

List<string> lStr = new List<string> {null, string.Empty, "0", "1", "41", "2", "3", "4", "5" };

var itmIsRemoved1 = lStr.Remove(lStr.FirstOrDefault(str => str != null));

var itmIsRemoved2 = lStr.Remove(lStr.FirstOrDefault(str => str == "4"));

var itmIsRemoved3 = lStr.Remove(lStr.FirstOrDefault(str => str == string.Empty));

var itmIsRemoved4 = lStr.Remove(lStr.FirstOrDefault(str => str == null));

您认为执行上述代码的每一行之后，'itmIsRemoved的值以及字符串列表中的值是什么?

What do you think the value of ''itmIsRemoved, and the values in the List of strings, are after each line of the code above is executed ?

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