下划线箭头(_ => ...)这是什么? [英] Underscore Arrow (_ => ...) What Is This?

问题描述

通俗易懂地阅读C#，我注意到了我从未遇到过的这段代码:

Reading through C# in a Nutshell I noticed this bit of code that I've never came across:

_uiSyncContent.Post(_ => txtMessage.Text += "Test");

下划线后接箭头是什么?我见过Lambda表达式以类似的方式编写，但是没有下划线.

What is that underscore followed by an arrow? I've seen Lambda expressions written in a similar way but nothing with an underscore.

推荐答案

这只是一个使用 _ 而不是 x 作为参数的lambda表达式. _ 是有效的标识符，因此可以用作参数名称.

It's just a lambda expression that uses _ instead of x for its parameter. _ is a valid identifier so it can be used as a parameter name.

正如评论中提到的那样，在某些开发人员中是一个惯例，称其为 _ 来表示它实际上不是由lambda表达式使用的，但仅此而已:惯例.

As mentioned in the comments, it's a convention among some developers to call it _ to indicate that it's not actually used by the lambda expression, but it's no more than that: a convention.

请注意，这与丢弃(在此答案问世几年后才引入)，这是一个特殊变量，用于分配将不使用的值，而将其丢弃.与丢弃的值不同， _ 参数在lambda范围内继续存在；在lambda表达式中的任何地方都没有使用它们.而且一次范围内只能有一个 _ .

Note that this is not the same thing as a discard (introduced several years after this answer), which is a special variable for assigning values that aren't going to be used and will instead be discarded. Unlike discarded values, _ parameters continue to exist in lambda scope; they just aren't used anywhere in the lambda expression. And there can only be one _ in scope at a time.

这篇关于下划线箭头(_ => ...)这是什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！