About Collections

[gitniupitang102]

You have created many interfaces, aliases, enumerations and structs in the library file. I can understand inheritance, implementation and methods in oop, but I can't understand the pointer code, especially when using the system's built-in interfaces. For example, the __SYSTEM instruction. I couldn't find these in Beckhoff's help manual, so it's very difficult for me to understand your code. Moreover, your FBS are all nested loops, which is really hard to understand.

[gitniupitang102]

And I have no idea about algorithms at all

[fisothemes]

Hi @gitniupitang102,

Thanks for opening the discussion. First of all I want to say that the code base is huge and there are a lot of advanced topics like pointers, memory management, DSA (Data Structures and Algorithms), error handling and interface-based programming. The reality is that I wouldn't be able to walk you through everything, it will take too long. The best I can do is jump start your journey.

The most important thing you can do right now is to become comfortable with pointers and understand how dynamic data structures like linked lists work. These concepts are the foundation of this library.

A good starting point is this simple video on Linked Lists. Try to implement it in structured text. Luckily TwinCAT has the__NEW and __DELETE operators. Play around with those. I recommend following examples in C/C++ and translate them into ST. It will give you a solid mental model. Leavarage AI models if you're stuck.

To help you get started a typical Node for a Singly Linked List would look like this:

{attribute 'enable_dynamic_creation'}
TYPE ST_Node:
STRUCT
    Data : INT;
    pNext : POINTER TO ST_Node;
END_STRUCT
END_TYPE

This defines a single node that holds an INT and a pointer to the next node.

Here's a basic program that creates 3 nodes and links them manually:

PROGRAM MAIN
// Create and initialise the nodes.
VAR
    stNode1 : ST_Node := (Data := 10);
    stNode2 : ST_Node := (Data := 20);
    stNode3 : ST_Node := (Data := 30);
END_VAR

// Link the nodes
stNode1.pNext := ADR(stNode2);
stNode2.pNext := ADR(stNode3);
stNode3.pNext := 0; // null pointer (tail of the list)

Run this and login into online mode and browser the inner symbols. You will see something interesting.

Now try to do this with the __NEW to allocate each node at runtime and __DELETE to free them. Use a state machine:

{attribute 'qualified_only'}
{attribute 'strict'}
{attribute 'to_string'}
TYPE E_State:
(
    Init := 0,
    Append,
    Remove,
    Clear
)BYTE;
END_TYPE

After that convery them to methods.

Click here for info on generic types.