Lambda表达式是表示匿名方法的一种简洁方式。匿名方法和Lambda表达式都允许您内联定义方法实现，但是，匿名方法显式地要求您定义方法的参数类型和返回类型。Lambda表达式使用c# 3.0的类型推断特性，该特性允许编译器根据上下文推断变量的类型。这是非常方便的，因为这节省了我们大量的输入!

创新在于类型的安全性和透明度。虽然您没有声明lambda表达式的类型，但它们是推断出来的，并且可以由代码搜索、静态分析、重构工具和运行时反射使用。

例如，在您使用SQL之前，可能会受到SQL注入攻击，因为黑客在通常需要数字的地方传递了一个字符串。现在您将使用LINQ lambda表达式，这是受保护的。

在纯委托上构建LINQ API是不可能的，因为它需要在计算表达式树之前将它们组合在一起。

2016年，大多数流行语言都支持lambda表达式，c#是主流命令式语言中这一演变的先驱之一。

很多时候，您只在一个地方使用功能，所以创建方法只会使类变得混乱。

Microsoft has given us a cleaner, more convenient way of creating anonymous delegates called Lambda expressions. However, there is not a lot of attention being paid to the expressions portion of this statement. Microsoft released a entire namespace, System.Linq.Expressions, which contains classes to create expression trees based on lambda expressions. Expression trees are made up of objects that represent logic. For example, x = y + z is an expression that might be part of an expression tree in .Net. Consider the following (simple) example:

using System;
using System.Linq;
using System.Linq.Expressions;


namespace ExpressionTreeThingy
{
    class Program
    {
        static void Main(string[] args)
        {
            Expression<Func<int, int>> expr = (x) => x + 1; //this is not a delegate, but an object
            var del = expr.Compile(); //compiles the object to a CLR delegate, at runtime
            Console.WriteLine(del(5)); //we are just invoking a delegate at this point
            Console.ReadKey();
        }
    }
}

This example is trivial. And I am sure you are thinking, "This is useless as I could have directly created the delegate instead of creating an expression and compiling it at runtime". And you would be right. But this provides the foundation for expression trees. There are a number of expressions available in the Expressions namespaces, and you can build your own. I think you can see that this might be useful when you don't know exactly what the algorithm should be at design or compile time. I saw an example somewhere for using this to write a scientific calculator. You could also use it for Bayesian systems, or for genetic programming (AI). A few times in my career I have had to write Excel-like functionality that allowed users to enter simple expressions (addition, subtrations, etc) to operate on available data. In pre-.Net 3.5 I have had to resort to some scripting language external to C#, or had to use the code-emitting functionality in reflection to create .Net code on the fly. Now I would use expression trees.

您还可以在编写作用于方法的泛型代码时使用lambda表达式。

例如:计算方法调用所花费的时间的泛型函数。(即这里的动作)

public static long Measure(Action action)
{
    Stopwatch sw = new Stopwatch();
    sw.Start();
    action();
    sw.Stop();
    return sw.ElapsedMilliseconds;
}

你可以使用lambda表达式调用上述方法，如下所示，

var timeTaken = Measure(() => yourMethod(param));

表达式允许您从方法和out参数中获取返回值

var timeTaken = Measure(() => returnValue = yourMethod(param, out outParam));

当我想使用另一个控件为某个控件的事件声明一个处理程序时，我发现它们很有用。 要做到这一点，你必须将控件的引用存储在类的字段中，这样你就可以在不同的方法中使用它们。

private ComboBox combo;
private Label label;

public CreateControls()
{
    combo = new ComboBox();
    label = new Label();
    //some initializing code
    combo.SelectedIndexChanged += new EventHandler(combo_SelectedIndexChanged);
}

void combo_SelectedIndexChanged(object sender, EventArgs e)
{
    label.Text = combo.SelectedValue;
}

多亏了lambda表达式，你可以这样使用它:

public CreateControls()
{
    ComboBox combo = new ComboBox();
    Label label = new Label();
    //some initializing code
    combo.SelectedIndexChanged += (s, e) => {label.Text = combo.SelectedValue;};
}

容易得多。