设置函数参数的默认值：

PS C:\Users\Administrator> function test{
>>     [CmdletBinding()]
>>     Param(
>>         [String]$username,
>>         [String]$type="direct"
>>     )
>>     $username
>>     $type
>> }
PS C:\Users\Administrator> get_memberslist -username "xiamingliang"
xiamingliang
direct
PS C:\Users\Administrator> get_memberslist -username "xiamingliang" -type "test"
xiamingliang
test
PS C:\Users\Administrator>
PS C:\Users\Administrator>