Default keywords in generic code

【Default keywords in generic code]

One problem that occurs in generic classes and generic methods is how to assign the default value to parameterized type T when the following conditions are unknown:

• T is the reference type or value type.

• If t is of the value type, whether it is a value or a structure.

Given a variable t of the parameterized type T, the Statement t = NULL is valid only when T is of the reference type; only when T is of the numerical type rather than the structure, statement t = 0 can be used normally. The solution is to use the default keyword,This keyword returns NULL for the reference type and zero for the value type. For the structure, this keyword returns each structure member whose Initialization is zero or null.Depends on whether the structure is a value type or a reference type. The following example from the genericlist <t> class shows how to use the default keyword. For more information, see generic overview.

public class GenericList<T>{    private class Node    {        //...        public Node Next;        public T Data;    }    private Node head;    //...    public T GetNext()    {        T temp = default(T);        Node current = head;        if (current != null)        {            temp = current.Data;            current = current.Next;        }        return temp;    }}

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Reference: http://msdn.microsoft.com/zh-cn/library/xwth0h0d (V = vs.90). aspx