Linked List Demo

[STxAxTIC]

Hello all,

Everyone knows the arrays-in-types issue can be subverted by linked lists, but not everyone embraces this (maybe two people I can name). I've been sitting on this "tech" for a while now, and realized a long time ago this this can be a hard swallow. What I've done here is implemented (one of) the simplest possible uses of this thing. We set up a simple type, insist that a string array be contained in the type there, and the rest is history. Just wanted to show, once more in 2020, how damn easy this can be. There is so much to explain, I've decided to explain none of it. Just see what the code is doing.

Code: QB64: [Select]

1. ' This program demonstrates using a linked list as a substitute for array in type.
2.  
3. OPTION _EXPLICIT
4.  
5. REM $Include: 'SoftArrays.bi'
6.  
7. ' *****************************
8. ' *** TYPEs and Definitions ***
9. ' *****************************
10.  
11. TYPE Person
12.     NickName AS STRING
13.     Country AS STRING
14.     FriendList AS SoftArrayStructure
15.     '             - Stores a Label for human readability.
16.     '             - Stores a LONG integer to denote place in memory.
17. END TYPE
18.  
19. DIM Steve AS Person
20.  
21. ' *******************************
22. ' *** Populate regular values ***
23. ' *******************************
24.  
25. Steve.NickName = "SMcNeill"
26. Steve.Country = "USA"
27.  
28. ' Nothing new so far, right? Confusion level: zero
29.  
30. ' **************************
31. ' *** Create linked list ***
32. ' **************************
33.  
34. Steve.FriendList.HeadNode = NewSoftArray("Steve's Friends")
35.  
36. ' This line initializes a linked list ^, and stores the head node address in Steve.FriendList.HeadNode.
37. ' Note we have not specified the size, the data it holds, etc.
38. ' The head node address is calculated automatically - think of it like an image handle.
39.  
40. ' ********************************
41. ' *** Structure of linked list ***
42. ' ********************************
43.  
44. ' Now we populate Steve's list of friends. The end result is going to look like:
45. '
46. '     Steve's Friends ------- Friend 1 (Joe)
47. '                                |
48. '                             Friend 2 (Tom)
49. '                                |
50. '                             Friend 3 (Biff)
51. '
52. ' Note that "Friend 1" appears to the "East" of the Label.
53. ' Note that "Frinds 2" appears to the "South" of Friend 1.
54. ' Note that "Frinds 3" appears to the "South" of Friend 2.
55.  
56. ' ****************************
57. ' *** Populate linked list ***
58. ' ****************************
59.  
60. ' Define a helper variable to keep the notation slim:
61. DIM a AS LONG
62.  
63. a = Steve.FriendList.HeadNode
64. a = LinkEast(a, NewTextNode("Joe"))
65. a = LinkSouth(a, NewTextNode("Tom"))
66. a = LinkSouth(a, NewTextNode("Biff"))
67.  
68. ' ... And that's it. The data is stored according to the structure above.
69. ' Each piece of data is stored in a Node, each with its own address.
70. ' The name of the game now is getting used to handling these addresses.
71.  
72. ' *************************
73. ' *** Print linked list ***
74. ' *************************
75.  
76. ' The following line will print the entire list, including the head node.
77.  
78. PRINT PrintSoftArray("Steve's Friends")
79. PRINT
80.  
81. ' ************************************
82. ' *** Retrieve first piece of data ***
83. ' ************************************
84.  
85. ' The very first item on the list can be printed by:
86.  
87. PRINT Literal$(Content("Steve's Friends"))
88. PRINT
89.  
90. ' ************************
91. ' *** Typical FOR loop ***
92. ' ************************
93.  
94. DIM j AS INTEGER
95. DIM b AS LONG
96. FOR j = 0 TO Bottom("Steve's Friends")
97.     PRINT Literal$(JumpFrom(Content("Steve's Friends"), "s", j))
98. NEXT
99. PRINT
100.  
101. END
102.  
103. REM $Include: 'SoftArrays.bm'
104.  

[SpriggsySpriggs]

Even though I responded to you on this on Discord, might as well give this a bump and let the forum-ites know what I was thinking about.
I saw where you replied to my code on mapped variables and said that the idea would/could work with your JSON writer. Makes me even more interested in what is going on with this. I hope more people take an interest into the idea since the way your code is laid out makes it easy for someone to take it up and learn about the parent-child relationships between the nodes. Looking forward to seeing more developments on this in the future.

[SpriggsySpriggs]

@STxAxTIC I think this will be useful for an EDI parser I'm writing but I'm needing some help getting started. The file is structured with a purchase order, then a part number, then the shipping terms, dates, and quantities. I want to store all that in an "object", which your library can do. I'm curious about how I'd dynamically retrieve the specific information I want. If I want all the shipping quantities from that part, how could I grab only that information from the structure? Thank you in advance.

[Qwerkey]

Everyone knows the arrays-in-types issue can be subverted by linked lists, but not everyone embraces this

Everyone??  Have not the slightest idea what you're talking about.  Better not tell Odin.  He'll erase my account.

[bplus]

Everyone??  Have not the slightest idea what you're talking about.  Better not tell Odin.  He'll erase my account.

Here is another discussion about having arrays in types: https://www.qb64.org/forum/index.php?topic=3977.0

and another https://www.qb64.org/forum/index.php?topic=915.msg101222#msg101222

and another https://www.qb64.org/forum/index.php?topic=841.msg100453#msg100453

Basically you store a bunch of info in a string and parse or read lengths of it for "array" values or store an array pointer in memory as Spriggsy says.