List as data contract in Custom AIF service Dynamics Ax 2012

During writing one of custom AIF services, I had requirement to get and set List of certain class type. For exampel Contact list if we have to import Customer or vendor, I found following syntax for attribute to make List as data contract.
[DataMemberAttribute("MyContactList"),
AifCollectionTypeAttribute("contactList",Types::Class, classStr(ContactDC)),
AifCollectionTypeAttribute("return",Types::Class, classStr(ContactDC))]
public List parmMyContactList(List contactList =_contactList)
{
_contactList = contactList;
return _contactList;
}