C# 3.0新特性体验之Lambda表达式

public myform()
{
　listbox = new listbox(...);
　textbox = new textbox(...);
　addbutton = new button(...);
　addbutton.click += new eventhandler(addclick);
}

void addclick(object sender, eventargs e)
{
　listbox.items.add(textbox.text);
}

public myform()
{
　listbox = new listbox(...);
　textbox = new textbox(...);
　addbutton = new button(...);
　addbutton.click += delegate
　{
　　listbox.items.add(textbox.text);
};

(int x) => x + 1 // 显式类型参数
(y,z) => return y * z; // 隐式类型参数

// program.cs
using system;
using system.collections.generic;
using system.text;
using system.query;
using system.xml.xlinq;
using system.data.dlinq;

namespace lambdaexample
{
　public delegate bool keyvaluefilter<k, v>(k key, v value);
　static class program
　{

　　static void main(string[] args)
　　{
　　　list<string> list = new list<string>();

　　　list.add("aa");
　　　list.add("abc");
　　　list.add("defg");
　　　list.add("xyz");
　　　console.writeline("through anonymous method");
　　　anonmethod(list);
　　　console.writeline("through lambda expression");
　　　lambdaexample(list);

　　　dictionary<string, int> varclothes= new dictionary<string,int>();

　　　varclothes.add("jeans", 20);
　　　varclothes.add("shirts", 15);
　　　varclothes.add("pajamas", 9);
　　　varclothes.add("shoes", 9);
　　　var clotheslistshortage = varclothes.filterby((string name,
　　　int count) => name == "shoes" && count < 10);
　　　// example of multiple parameters
　　　if(clotheslistshortage.count > 0)
　　　　console.writeline("we are short of shoes");
　　　console.readline();
　}

　static void anonmethod(list<string> list)
　{
　　list<string> evennumbers = list.findall(delegate(string i)
　　{ return (i.length % 2) == 0; });
　　foreach (string evennumber in evennumbers)
　　{
　　　console.writeline(evennumber);
　　}
　}

　static void lambdaexample(list<string> list)
　{
　　var evennumbers = list.findall(i =>(i.length % 2) == 0); // example of single parameter
　　foreach(string i in evennumbers)
　　{
　　　console.writeline(i);
　　}
　}
}

public static class extensions
{
　public static dictionary<k, v> filterby<k, v>
(this dictionary<k, v> items, keyvaluefilter<k, v> filter)
　{
　　var result = new dictionary<k, v>();
　　foreach(keyvaluepair<k, v> element in items)
　　{
　　　if (filter(element.key, element.value))
　　　　result.add(element.key, element.value);
　　}
　　return result;
　}
　
}
}

c:/program files/linq preview/bin/csc.exe
/reference:"c:/program files/linq preview/bin/system.data.dlinq.dll"
/reference:c:/windows/microsoft.net/framework/v2.0.50727/system.data.dll
/reference:c:/windows/microsoft.net/framework/v2.0.50727/system.dll
/reference:"c:/program files/linq preview/bin/system.query.dll"
/reference:c:/windows/microsoft.net/framework/v2.0.50727/system.xml.dll
/reference:"c:/program files/linq preview/bin/system.xml.xlinq.dll"
/target:exe program.cs

.method private hidebysig static void anonmethod(class
[mscorlib]system.collections.generic.list`1<string> list)
cil managed
{
　// code size 96 (0x60)
　.maxstack 4
　.locals init ([0] class [mscorlib]system.collections.generic.list
　`1<string> evennumbers,
　[1] string evennumber,
　[2] valuetype [mscorlib]system.collections.generic.list
　`1/enumerator<string> cscode_replacement 000,
　[3] bool cscode_replacement 001)
　il_0000: nop
　il_0001: ldarg.0
　il_0002: ldsfld class [mscorlib]system.predicate
　`1<string> lambdaexample.program::
　`<>9__cachedanonymousmethoddelegate1'
　il_0007: brtrue.s il_001c
　il_0009: ldnull
　il_000a: ldftn bool lambdaexample.program::
　`<anonmethod>b__0'(string)
　il_0010: newobj instance void class [mscorlib]system.predicate
　`1<string>::.ctor(object, native int)
　il_0015: stsfld class [mscorlib]system.predicate`1<string>
　lambdaexample.program::
　`<>9__cachedanonymousmethoddelegate1'
　il_001a: br.s il_001c
　il_001c: ldsfld class [mscorlib]system.predicate`1<string>
　lambdaexample.program::'<>
　9__cachedanonymousmethoddelegate1'
　il_0021: callvirt instance class [mscorlib]system.collections.
　generic.list`1<!0> class [mscorlib]system.
　collections.generic.list`1<string>::
　findall(class [mscorlib]system.predicate`1<!0>)
　il_0026: stloc.0
　il_0027: nop
　il_0028: ldloc.0
　il_0029: callvirt instance valuetype [mscorlib]system.collections.
　generic.list`1/enumerator<!0> class
　[mscorlib]system.collections.generic.list`1
　<string>::getenumerator()
　il_002e: stloc.2
　.try
　{
　　il_002f: br.s il_0042
　　il_0031: ldloca.s cscode_replacement 000
　　il_0033: call instance !0 valuetype [mscorlib]system.
　　collections.generic.list`1/enumerator
　　<string>::get_current()
　　il_0038: stloc.1
　　il_0039: nop
　　il_003a: ldloc.1
　　il_003b: call void [mscorlib]system.console::
　　writeline(string)
　　il_0040: nop
　　il_0041: nop
　　il_0042: ldloca.s cscode_replacement 000
　　il_0044: call instance bool valuetype [mscorlib]system.
　　collections.generic.list`1/enumerator
　　<string>::movenext()
　　il_0049: stloc.3
　　il_004a: ldloc.3
　　il_004b: brtrue.s il_0031
　　il_004d: leave.s il_005e
　} // end .try
　finally
　{
　　il_004f: ldloca.s cscode_replacement 000
　　il_0051: constrained. valuetype [mscorlib]system.collections.
　　generic.list`1/enumerator<string>
　　il_0057: callvirt instance void [mscorlib]system.
　　idisposable::dispose()
　　il_005c: nop
　　il_005d: endfinally
　} // end handler
　il_005e: nop
　il_005f: ret
} // end of method program::anonmethod

var clotheslistshortage = clotheslist.filterby((string name, int count)
=> name == "shoes" && count < 10);