你可以解释lambda表达式吗？ [英] Can you explain lambda expressions?

问题描述

我真的不获得 lambda表达式。自从ALGOL的日子开始，我们才开始听到他们的观点，直到最近才发现Python和Ruby变得非常受欢迎。现在C＃有 => 语法，我的世界（.NET）中的人越来越多地在谈论lamdba表达式。

I don't really get lambda expressions. While they've been around since the days of ALGOL, I didn't start hearing about them until fairly recently, when Python and Ruby became very popular. Now that C# has the => syntax, people in my world (.NET) are talking about lamdba expressions more and more.

我已经阅读了关于lambda演算的维基百科文章，但我并不是一个数学家。从实际的角度来看，我真的不了解它。什么时候我会使用lambda表达式？为什么？我如何知道这是我应该在做什么？

I've read the Wikipedia article on the lambda calculus, but I'm not really a math guy. I don't really understand it from a practical perspective. When would I use lambda expressions? Why? How would I know that it's what I should be doing?

你能否以前后格式显示如何解决lambda表达式问题的示例？任何命令式语言都很好，但C＃对我来说最容易理解。

Can you show examples of how you would solve problems with lambda expressions, in a before-and-after format? Any imperative language is fine, but C# would be easiest for me to understand.

推荐答案

基本上，就C＃而言，lambda表达式是创建代理（或表达式树，但现在让我们放在一边的）的简单方法。

Basically as far as C# is concerned, lambda expressions are an easy way to create a delegate (or an expression tree, but let's leave those aside for now).

在C＃1中，我们只能从正常创建委托实例方法。
在C＃2中，我们获得了匿名方法。
在C＃3中，我们获得了lambda表达式，这就像更简洁的匿名方法。

In C# 1 we could only create delegate instances from normal methods. In C# 2 we gained anonymous methods. In C# 3 we gained lambda expressions, which are like more concise anonymous methods.

当你想表达一些需要一个逻辑的逻辑时，它们特别简洁值并返回一个值。例如，在LINQ的上下文中：

They're particularly concise when you want to express some logic which takes one value and returns a value. For instance, in the context of LINQ:

                       // Only include children - a predicate
var query = dataSource.Where(person => person.Age < 18) 
                       // Transform to sequence of names - a projection
                      .Select(person => person.Name);

有一个更全面的讨论与其他方面 - 关于关闭的文章。

There's a fuller discussion of this - along with other aspects - in my article on closures.

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