yield关键字, default关键字, 别名关键字
1.yield返回IEnumberable接口对象,使其可以支持foreach迭代。
yeild return用于返回值,yeild break用于中断迭代。
迭代器的返回类型必须为IEnumerable、IEnumerator、IEnumerable<T>或IEnumerator<T>。
如:
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/None.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBlockStart.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/InBlock.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/InBlock.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/InBlock.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/InBlock.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubBlockStart.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/InBlock.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/InBlock.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubBlockEnd.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubBlockEnd.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBlockEnd.gif)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/None.gif)
2. default(int)
3.using colAlias = System.Collections;
colAlias::Hashtable test = new colAlias::Hashtable();