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What data type would you prefer?

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  • User profile image
    Sathyaish Chakravarthy

    I wanted to practice some Linked List stuff, so I set out to create a linked list. The  plan was to create the following:

    1. A linked list class in Visual Basic
    2. A non-class based linked list using functions in C
    3. A linked list class in C++
    I started with Visual Basic and I wrote an IList interface that I wanted my list to  implement. When I had started, somehow I thought this time, I'd first use a  collection as the ingredient, and so it would not really be a linked list. It would be  an extended collection behaving like a (not linked, but just a) list, as in list of  things. And my new agenda would then be,

    1. A list (not a linked list) class in Visual Basic by extending the Collection object.
    2. A linked list class in Visual Basic
    3. A linked list in Visual Basic that is not class-based but has a struct (Type) and  global functions in a standard module (.bas).
    4. A non-class based linked list using functions in C
    5. A linked list class in C++

    I don't like to create lists if they have no meaning, so I thought it would be a good  idea if the list was a list of something and not just "ints". So, I made a list of members I know on the Joel On Software forum. I called the list MyFriends.

    I have just finished implementing a list by extending the Visual Basic's Collection object. My list has the following interface:

    Public Function
    AddAtPos(ByRef Object As Object, _
    ByVal Index As Long) As Boolean
    End Function

    Public Function PeekAtPos(ByVal Index As Long) As Object
    End Function

    Public Function RemoveAtPos(ByVal Index As Long) As Boolean
    End Function

    Public Property Get Count() As Long
    End Property

    Public Function
    Contains(Object As Object) As Boolean
    End Function

    Public Function IndexOf(Object As Object) As Long
    End Function

    Public Sub Serialize()
    End Sub

    Public Sub
    End Sub

    Public Sub Clear()
    End Sub

    Public Sub Sort(ByVal SortOrder As SortOrders)
    End Sub

    Public Sub Reverse()
    End Sub

    Source Code

    If you're interested, you can find the source code and the executable for my first  experiment here.


    Now, I am set to implement item number (2) in my agenda - the linked list class in  Visual Basic. Once again, the semantics remain the same. I intend to keep the list  as a list of friends. So each node in the list is a friend. While designing the "node"  class or the "MyFriend" class, I stumbled accross this problem. I am recording two  pieces of information about each friend:
    1. Name
    2. Phone Number
    Both are of String type. The problem was not with these, but with the "node  pointer" item. I have three data types in mind that I can use to point to the next  node. I am confused as to which one would be a good choice, and I want your  opinion on the same.

    Here's what I have thought the node/MyFriend class as:

    MyFriend Class

    Implements IList

    Private mName As String
    mPhoneNumber As String

    '===Which one do I choose?=======
    'Private mNextFriend As MyFriend
    '         OR
    'Private mNextFriend As Long
    '         OR
    'Private mNextFriend() As Byte

    Let me argue each case, as I thought about them. Starting with the last, if I take  the mNextFriend field as a Byte array, it would help nothing, basically.  So, ruled out.

    Next, if took the mNextFriend field as a Long, I think it would be the ideal thing  to do, because VB6 Long's are indeed 32-bit values, and then I would use the  mNextFriend Long field to point to a new instance of MyFriend type, using the  ObjPtr function. I would dereference the mNextFriend Long type by using  RtlMoveMemory. That sounds like a nice plan. However, the problem with this is  that it does not strictly confirm to a Linked List set up, because of the generic  nature of this Long pointer. This pointer could be used to point not only to  MyFriend types but to anything. Since I am going to be the developer audience  for this class, and hence this is only dogfood, it is no problem, but in general, I  don't like it as a habit and I always want my code to represent what it ought to  represent. So, this would be like compromising on a trivial issue.

    If I use mNextFriend as a MyFriend type, I solve the problem of the generic  pointer by restricting it to the MyFriend type. So, it's more disciplined this way,  but now, the field is not really a pointer. It is an object. Of course, it is still a 32-bit  reference to the actual object, but it is still not a real pointer.

    So, I am confused. If you were to be doing this, what option would you choose  and why? To me, the Long seems like ok, although it is a little bit of a  compromise on the type-checking.

  • User profile image

    I think you can find more people ready to answer on tech forum, if you already posted there never mind. Just wanted to make sure you know that there is a forum specifically for these type of questions.

  • User profile image
    Sathyaish Chakravarthy

    I did know about it but before I made this post, it didn't occur to me. Sorry, I just forgot about the tech forum.

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