检查空值的正确方法是什么? [英] What is the proper way to check for null values?

问题描述

我喜欢空合并运算符，因为它可以轻松地为可空类型分配默认值.

I love the null-coalescing operator because it makes it easy to assign a default value for nullable types.

 int y = x ?? -1;

那太好了，除非我需要用 x 做一些简单的事情.例如，如果我想检查 Session，那么我通常最终不得不写一些更详细的东西.

That's great, except if I need to do something simple with x. For instance, if I want to check Session, then I usually end up having to write something more verbose.

我希望我能做到这一点:

I wish I could do this:

string y = Session["key"].ToString() ?? "none";

但是你不能，因为 .ToString() 在空检查之前被调用，所以如果 Session["key"] 为空，它会失败.我最终这样做了:

But you can't because the .ToString() gets called before the null check so it fails if Session["key"] is null. I end up doing this:

string y = Session["key"] == null ? "none" : Session["key"].ToString();

在我看来，它比三行替代方案更有效:

It works and is better, in my opinion, than the three-line alternative:

string y = "none";
if (Session["key"] != null)
    y = Session["key"].ToString();

即使这样有效，我仍然很好奇是否有更好的方法.似乎不管我总是要引用 Session["key"] 两次；一次是检查，一次是分配.有什么想法吗?

Even though that works I am still curious if there is a better way. It seems no matter what I always have to reference Session["key"] twice; once for the check, and again for the assignment. Any ideas?

推荐答案

怎么样

string y = (Session["key"] ?? "none").ToString();

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