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【中文问题版本】
.NET中泛型通常遵循â先定义，后使用â原则ââ比如系统预定义的Func带有返回值的委托，你必须：
Func<int,int> j=(i)=>i;
而不能：
Func<int,？> j=(i)=>i; //因为这里会报告T没有定义âââ这里？表示空缺，是不允许的â。
但是我注意到几乎所有的扩展函数（比如Select函数）ââ
int[]numbers=ââ//省略定义
numbers.Select(i=>i); 注意，Select里边需要一个Func<TSource,TResult>，但是此处TResult在上面例子中貌似没有定义啊？你没有告诉它是int还是什么类型。
难道说：
1）在扩展函数情况下，允许省略定义直接使用，NET的CLR会直接感知出来？
2）此类情况还作用于哪些情况下？
3）既然Select是需要一个Func<TSource,TResult>的委托，那么我可以显示写成Select<类型1，类型2>(i=>i);来调用吗？那么1和3的情况的差别何在啊？
<pre style="background:white; color:black; font-family:NSimSun <span style="color:blue int[] <span>numbers <span>= { <span>1,<span>2,<span>3,<span>4,<span>5};<br/><span>numbers<span>.<span>Select<span><<span style="color:blue int, <span style="color:blue string<span>>(<span>i <span>=> <span>i<span>.<span>ToString());[/code]
【English Version】
In .NET framework, You should define the specific generic to tell which type(s) you are going to use before they are usedââLets take the .NETs pre-defined functionââFunc for an example：
Func<int,int> j=(i)=>i;
But you cannot sayââ
Func<int,？> j=(i)=>i; //No defination for ？, so this is invalid, which will cause a syntax error.
But Ive noticed nearly all the extended method (since net framework 3.5)ââ
int[]numbers=ââ//omit defination hereââ
numbers.Select(i=>i); //"Select" needs a delegate of Func<TSource,TResult>，but wheres the defination for "TResult" in the above sample？You havent told it whether its of int or some other type？
Can I think：
1）In the extended method，we can use it before defination and NETsCLR will know that type？
2）Where can I also see such situation of "intellisensely-telling type for a generic type"？
3）Since "Select" is a delegate that needs Func<TSource,TResult>，I can also define exclipitly it as "Select<type1，type2>(i=>i);"
<br/>
Can I use like that？Whats the difference between 1 and 3？Sample looks like below：
<pre style="background:white; color:black; font-family:NSimSun <span style="color:blue int[] <span>numbers <span>= { <span>1,<span>2,<span>3,<span>4,<span>5};<br/><span>numbers<span>.<span>Select<span><<span style="color:blue int, <span style="color:blue string<span>>(<span>i <span>=> <span>i<span>.<span>ToString());[/code]
<
http://mail.qq.com/cgi-bin/qm_share?t=qm_mailme&email=-JGdkJmYk5Kbo4yOlYqdiJm8jY3Sn5OR" target="_blank <img src="http://rescdn.qqmail.com/zh_CN/htmledition/images/function/qm_open/ico_mailme_02.png" alt=" QQ我： http://sighttp.qq.com/authd?IDKEY=c5a1e2c9ea4f0b16c65453c0116275d7eded425641624137" target="_blank <img title="讨论(Talk)" src="http://wpa.qq.com/imgd?IDKEY=c5a1e2c9ea4f0b16c65453c0116275d7eded425641624137&pic=46 &r=0.7423044074346896" border="0" alt="讨论(Talk)
<br/>
http://msdn.microsoft.com/zh-cn/gg650455.aspx?ocid=ban-f-cn-wag-20110225-MSDN&ocid=soc-f-cn-win--SINA 下载MSDN桌面工具(Vista,Win7)
<br/>
http://www.cnblogs.com/ServiceboyNew/ 我的博客园 <br/>
http://www.bushinet.com/dj/ 慈善点击，点击此处 <br/>
View the full article
.NET中泛型通常遵循â先定义，后使用â原则ââ比如系统预定义的Func带有返回值的委托，你必须：
Func<int,int> j=(i)=>i;
而不能：
Func<int,？> j=(i)=>i; //因为这里会报告T没有定义âââ这里？表示空缺，是不允许的â。
但是我注意到几乎所有的扩展函数（比如Select函数）ââ
int[]numbers=ââ//省略定义
numbers.Select(i=>i); 注意，Select里边需要一个Func<TSource,TResult>，但是此处TResult在上面例子中貌似没有定义啊？你没有告诉它是int还是什么类型。
难道说：
1）在扩展函数情况下，允许省略定义直接使用，NET的CLR会直接感知出来？
2）此类情况还作用于哪些情况下？
3）既然Select是需要一个Func<TSource,TResult>的委托，那么我可以显示写成Select<类型1，类型2>(i=>i);来调用吗？那么1和3的情况的差别何在啊？
<pre style="background:white; color:black; font-family:NSimSun <span style="color:blue int[] <span>numbers <span>= { <span>1,<span>2,<span>3,<span>4,<span>5};<br/><span>numbers<span>.<span>Select<span><<span style="color:blue int, <span style="color:blue string<span>>(<span>i <span>=> <span>i<span>.<span>ToString());[/code]
【English Version】
In .NET framework, You should define the specific generic to tell which type(s) you are going to use before they are usedââLets take the .NETs pre-defined functionââFunc for an example：
Func<int,int> j=(i)=>i;
But you cannot sayââ
Func<int,？> j=(i)=>i; //No defination for ？, so this is invalid, which will cause a syntax error.
But Ive noticed nearly all the extended method (since net framework 3.5)ââ
int[]numbers=ââ//omit defination hereââ
numbers.Select(i=>i); //"Select" needs a delegate of Func<TSource,TResult>，but wheres the defination for "TResult" in the above sample？You havent told it whether its of int or some other type？
Can I think：
1）In the extended method，we can use it before defination and NETsCLR will know that type？
2）Where can I also see such situation of "intellisensely-telling type for a generic type"？
3）Since "Select" is a delegate that needs Func<TSource,TResult>，I can also define exclipitly it as "Select<type1，type2>(i=>i);"
<br/>
Can I use like that？Whats the difference between 1 and 3？Sample looks like below：
<pre style="background:white; color:black; font-family:NSimSun <span style="color:blue int[] <span>numbers <span>= { <span>1,<span>2,<span>3,<span>4,<span>5};<br/><span>numbers<span>.<span>Select<span><<span style="color:blue int, <span style="color:blue string<span>>(<span>i <span>=> <span>i<span>.<span>ToString());[/code]
<
http://mail.qq.com/cgi-bin/qm_share?t=qm_mailme&email=-JGdkJmYk5Kbo4yOlYqdiJm8jY3Sn5OR" target="_blank <img src="http://rescdn.qqmail.com/zh_CN/htmledition/images/function/qm_open/ico_mailme_02.png" alt=" QQ我： http://sighttp.qq.com/authd?IDKEY=c5a1e2c9ea4f0b16c65453c0116275d7eded425641624137" target="_blank <img title="讨论(Talk)" src="http://wpa.qq.com/imgd?IDKEY=c5a1e2c9ea4f0b16c65453c0116275d7eded425641624137&pic=46 &r=0.7423044074346896" border="0" alt="讨论(Talk)
<br/>
http://msdn.microsoft.com/zh-cn/gg650455.aspx?ocid=ban-f-cn-wag-20110225-MSDN&ocid=soc-f-cn-win--SINA 下载MSDN桌面工具(Vista,Win7)
<br/>
http://www.cnblogs.com/ServiceboyNew/ 我的博客园 <br/>
http://www.bushinet.com/dj/ 慈善点击，点击此处 <br/>
View the full article
