你能解释lambda表达式吗？ [英] Can you explain lambda expressions?

问题描述

我实际上不会得到 lambda表达式。虽然他们从ALGOL的日子开始，直到最近，当Python和Ruby变得非常受欢迎，我才开始听到他们。现在C＃有 => 语法，我的世界中的人（.NET）越来越多地谈论lamdba表达式。

我读过维基百科上关于lambda演算的文章，但我不是一个数学家。我从一个实际的角度不真正理解它。我什么时候使用lambda表达式？为什么？我将如何知道这是我应该做什么？

你能展示一个如何解决lambda表达式的问题的例子，在一个前后格式？任何命令式语言都很好，但C＃是最容易理解的。

解决方案

基本上就C＃表达式是一种创建委托（或表达式树，但现在让我们暂时离开）的简单方法。

在C＃1中，我们只能从普通方法。
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。

当你想表达一些逻辑，值并返回一个值。例如，在LINQ的上下文中：

  //只包含子项 - 一个谓词
 var query = dataSource。 where（person => person.Age< 18）
 //转换为名称序列 - 投影
 .Select（person => person.Name）; 
  
 
 
 
有关这一点以及其他方面的更全面的讨论在关于关闭的文章。
 
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.

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?

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.
解决方案
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).

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.

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

                        
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