.Net分析与设计
1.0中首先声明一个委托类型，再定义一个相同签名的方法，就可以用了。
1
class Test
2
{
3
delegate double Calc(double x);
4
5 static void Main(string[] args)
6
{
7 double[] a = { 0.0, 0.5, 1.0 };
8 double[] results = Apply(a, new Calc(Square));
9 foreach (double d in results)
10 {
11 Console.WriteLine(d);
12
}
13
14 Console.ReadLine();
15 }
16
17 public static double Square(double x)
18 {
19 return x * x;
20 }
21
22 static double[] Apply(double[] a, Calc f)
23 {
24 double[] result = new double[a.Length];
25 for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);
26 return result;
27 }
28
}
整个代码虽然比较繁琐，但确很明了。class Test2
{3
delegate double Calc(double x);4
5
static void Main(string[] args)6
{7
double[] a = { 0.0, 0.5, 1.0 };8
double[] results = Apply(a, new Calc(Square));9
foreach (double d in results)10
{11
Console.WriteLine(d);12
}13
14
Console.ReadLine();15
}16
17
public static double Square(double x)18
{19
return x * x;20
}21
22
static double[] Apply(double[] a, Calc f)23
{24
double[] result = new double[a.Length];25
for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);26
return result;27
}28
}自从2.0推出了匿名方法之后，上面的写法就不够紧跟时代潮流了，应该这么写了：
1class Test
2{
3 delegate double Calc(double x);
4
5 static void Main(string[] args)
6 {
7 double[] a = { 0.0, 0.5, 1.0 };
8 double[] results = Apply(a, delegate(double x) { return x * x; });
9 foreach (double d in results)
10 {
11 Console.WriteLine(d);
12 }
13
14 Console.ReadLine();
15 }
16
17 static double[] Apply(double[] a, Calc f)
18 {
19 double[] result = new double[a.Length];
20 for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);
21 return result;
22 }
23}
代码是变少了，但是说实话，有的时候看这样的代码怎么好像就突然看不明白了呢？class Test2
{3
delegate double Calc(double x);4
5
static void Main(string[] args)6
{7
double[] a = { 0.0, 0.5, 1.0 };8
double[] results = Apply(a, delegate(double x) { return x * x; });9
foreach (double d in results)10
{11
Console.WriteLine(d);12
}13
14
Console.ReadLine();15
}16
17
static double[] Apply(double[] a, Calc f)18
{19
double[] result = new double[a.Length];20
for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);21
return result;22
}23
}即使这样，微软还是不放过像我这样脑袋不太好使的同志，它竟然推出了Lambda表达式，也就是说，上面的代码也不够先进了，应该这样了：
1class Test
2{
3 delegate double Calc(double x);
4
5 static void Main(string[] args)
6 {
7 double[] a = { 0.0, 0.5, 1.0 };
8 double[] results = Apply(a, x => x * x);
9 foreach (double d in results)
10 {
11 Console.WriteLine(d);
12 }
13
14 Console.ReadLine();
15 }
16
17 static double[] Apply(double[] a, Calc f)
18 {
19 double[] result = new double[a.Length];
20 for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);
21 return result;
22 }
23}
那一行代码彻底让我抓狂了，代码可以简洁到这种地步，语法竟然变化这么快，微软简直太牛了！class Test2
{3
delegate double Calc(double x);4
5
static void Main(string[] args)6
{7
double[] a = { 0.0, 0.5, 1.0 };8
double[] results = Apply(a, x => x * x);9
foreach (double d in results)10
{11
Console.WriteLine(d);12
}13
14
Console.ReadLine();15
}16
17
static double[] Apply(double[] a, Calc f)18
{19
double[] result = new double[a.Length];20
for (int i = 0; i < a.Length; i++) result[i] = f(a[i]);21
return result;22
}23
}但是，你如果看一下这三段代码的IL时，你就会发现它们几乎是一模一样的，不一样的仅仅是后面两段代码在编译的时候，编译器自动为我们生成了一个方法。
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