C#泛型

使用泛型的好处

type safety, 

所有类型相同, 减少编译报错

no casting, 

无需转换, 降低性能开销

no boxing and unboxing.

可以避免装箱拆箱, 减低性能消耗

泛型约束

Constraint	Description
where T : <name of interface>	The type argument must be, or implement, the specified interface.
where T : <name of base class>	The type argument must be, or derive from, the specified class
where T : U	The type argument must be, or derive from, the supplied type argument U
where T : new()	The type argument must have a public default constructor
where T : struct	The type argument must be a value type
where T : class	The type argument must be a reference type