public void Test()
{
UserTypeList userCollection = new UserTypeList();
IUserTypeList <UserType> IUserCollection = userCollection;
userCollection.Add(new UserType()
{
B = 1, U = 2
});
userCollection.Add(new UserType()
{
B = 3, U = 4
});
IUserTypeList <BaseType> IBaseCollection = userCollection;
BaseType b = IBaseCollection[0];
}