3月4日18时，中央气象台发布大雾黄色预警，浙江福建广西广东等地部分地区有大雾，能见度不足1公里。
When we define our interfaces in C# 4.0, we are allowed to mark each of the generic parameters as in or out. If we try to set a generic parameter as out and that\'d lead to a problem, the compiler rai
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