goto，可以说是程序界，名声最差的关键字之一了。有人强烈要求，在高级语言中，应该被和谐掉。
如果，你在满是高级业务逻辑的代码里，写上些goto，就好比，你在代码里，嵌了些汇编语言(goto应该待它自己的世界).
其实，我们常用的switch语句中，goto也若隐若现。请参考MSDN关于switch的说明文档。
现在，我分析一下，我们为啥要用switch语句：
先从一个简单的例子入手：
[Test(Description="switch可以被if等价代替")]
public void T1()
{
int x = 6;
//if语句
if (x % 2 == 0)
{
Console.WriteLine("偶数");
}
else if (x % 2 == 1)
{
Console.WriteLine("奇数");
}
else
{
Console.WriteLine("未知数");
}
//等价的switch语句
switch (x % 2)
{
case 0: Console.WriteLine("偶数"); break;
case 1: Console.WriteLine("奇数"); break;
default: Console.WriteLine("未知数");
break;
}
}
可以看出，if与switch几乎没啥区别，纯属个人爱好！
再举个例子：
[Test(Description="可能用到switch的地方")]
public void T2()
{
int x = 6;
//if语句分支太多!
if (x == 0)
{
Console.WriteLine("x=0");
}
else if (x == 1 || x == 2 || x == 3 || x == 4)
{
Console.WriteLine("0<x<5");
}
else if (x == 5)
{
Console.WriteLine("x=5");
}
else if (x == 6 || x == 7 || x == 8 || x == 9)
{
Console.WriteLine("5<x<10");
}
else
{
Console.WriteLine("x<0 or x>9");
}
//用switch语句更清晰?
switch (x)
{
case 0: Console.WriteLine("x=0"); break;
case 1:
case 2:
case 3:
case 4: Console.WriteLine("0<x<5"); break;
case 5: Console.WriteLine("x=5"); break;
case 6:
case 7:
case 8:
case 9: Console.WriteLine("5<x<10"); break;
default: Console.WriteLine("x<0 or x>9");
break;
}
}
可以看出，遇到这种情况，switch看起来还不错！
现在，我想用用switch的"高级"功能：
[Test(Description="可以作为糟糕的笔试题")]
public void T3()
{
int x = 6;
switch (x)
{
case 0: Console.WriteLine("x=0"); goto case 0;//while(true)!!!
case 1:
case 2:
case 3:
case 4: Console.WriteLine("0<x<5"); goto default;
case 5: Console.WriteLine("x=5"); break;
case 6:
case 7:
case 8:
case 9: Console.WriteLine("5<x<10"); goto case 1;
default: Console.WriteLine("x<0 or x>9");
break;
}
}
你可以在30"之内，"算"出结果吗？
我真正想说的是，除了if...else...与switch外，我们仍然有选择的余地：
[Test(Description="干掉switch语句")]
public void T4()
{
//我用Dictionary来组织这些规则，可以自定义更高级的类
var rules = new Dictionary<Predicate<int>, Action>
{
{x => x==0, ()=>Console.WriteLine("x=0")},
{x => 0<x&&x<5, ()=>Console.WriteLine("0<x<5")},
{x => x==5, ()=>Console.WriteLine("x=5")},
{x => 5<x&&x<10, ()=>Console.WriteLine("5<x<10")},
{x => x<0&&9<x, ()=>Console.WriteLine("x<0 or x>9")},
{x => true, ()=>Console.WriteLine("默认")}
};
int y = 6;
//找出所有满足要求的规则
rules.Where(x => x.Key(y)).each(x => x.Value());
//只找出一条满足要求的规则
rules.First(x => x.Key(y)).Value();
}
用Predicate/Action就解决了问题，感觉还好吗？
注：
在面向对象编程中，switch还涉及到很多重构，可以参考http://www.refactoring.com/catalog/index.html
附录：
代码
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NUnit.Framework;
namespace KSharp
{
[TestFixture]
public class TestSwitch
{
[Test(Description="switch可以被if代替")]
public void T1()
{
int x = 6;
//if语句
if (x % 2 == 0)
{
Console.WriteLine("偶数");
}
else if (x % 2 == 1)
{
Console.WriteLine("奇数");
}
else
{
Console.WriteLine("未知数");
}
//等价的switch语句
switch (x % 2)
{
case 0: Console.WriteLine("偶数"); break;
case 1: Console.WriteLine("奇数"); break;
default: Console.WriteLine("未知数");
break;
}
}
[Test(Description="可能用到switch的地方")]
public void T2()
{
int x = 6;
//if语句分支太多!
if (x == 0)
{
Console.WriteLine("x=0");
}
else if (x == 1 || x == 2 || x == 3 || x == 4)
{
Console.WriteLine("0<x<5");
}
else if (x == 5)
{
Console.WriteLine("x=5");
}
else if (x == 6 || x == 7 || x == 8 || x == 9)
{
Console.WriteLine("5<x<10");
}
else
{
Console.WriteLine("x<0 or x>9");
}
//用switch语句更清晰?
switch (x)
{
case 0: Console.WriteLine("x=0"); break;
case 1:
case 2:
case 3:
case 4: Console.WriteLine("0<x<5"); break;
case 5: Console.WriteLine("x=5"); break;
case 6:
case 7:
case 8:
case 9: Console.WriteLine("5<x<10"); break;
default: Console.WriteLine("x<0 or x>9");
break;
}
}
[Test(Description="可以作为笔试题")]
public void T3()
{
int x = 6;
switch (x)
{
case 0: Console.WriteLine("x=0"); goto case 0;//while(true)!!!
case 1:
case 2:
case 3:
case 4: Console.WriteLine("0<x<5"); goto default;
case 5: Console.WriteLine("x=5"); break;
case 6:
case 7:
case 8:
case 9: Console.WriteLine("5<x<10"); goto case 1;
default: Console.WriteLine("x<0 or x>9");
break;
}
}
[Test(Description="干掉switch语句")]
public void T4()
{
//我用Dictionary来组织这些规则，可以自定义更高级的类
var rules = new Dictionary<Predicate<int>, Action>
{
{x => x==0, ()=>Console.WriteLine("x=0")},
{x => 0<x&&x<5, ()=>Console.WriteLine("0<x<5")},
{x => x==5, ()=>Console.WriteLine("x=5")},
{x => 5<x&&x<10, ()=>Console.WriteLine("5<x<10")},
{x => x<0&&9<x, ()=>Console.WriteLine("x<0 or x>9")},
{x => true, ()=>Console.WriteLine("默认")}
};
int y = 6;
//找出所有满足要求的规则
rules.Where(x => x.Key(y)).each(x => x.Value());
//只找出一条满足要求的规则
rules.First(x => x.Key(y)).Value();
}
[Test]
public void T5()
{
//TODO:实现一般的业务规则类，其中可包括优先级等
}
}
}
原文地址：http://www.cnblogs.com/k-sharp/archive/2010/07/01/1769125.html