Yup, the last company where I worked I did a lot of OOP especially using thinks like Java, Ruby, C++, etc., and now I am programming in Structured Text. At least it's not LD.

Anyway, the short story is that I/d like to declare a global type so that I don't have to redeclare it in each function block. Something like...

TYPE CONTROL
STRUCT
A: INT;
B: BOOL;
END_STRUCT
END_TYPE

and in Main, declare...

VAR X: CONTROL; END_VAR

while in a function block,

VAR_IN_OUT Z: CONTROL ; END_VAR
...
Z.A := 4;
...

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The idea is to create an object with attached methods. The problem, as I see it with function blocks is that each one represents a single method. But upon aggregation one could create a class with objects from it by instantiating the structure; I can live without inheritance because these codes are quite tame compared to a GUI implementation, for example.

However, this becomes quite difficult without the ability to create a global type declaration. I <i>know</i> it's possible, there are control structures defined in the AB libraries...

Perhaps I'm getting this whole idea quite wrong and should approach it from another direction.

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OK, I see this is done using "actions."

You declare everything within the function block, and then instantiate it, and can call actions. This makes sense but it's a bit awkward, because typically object oriented stuff is written in the sense...
football.kick;
where football is the noun- the object, and kick is the verb. Their technique leaves one to create a default action for the function block, in other words:
football;
does something... but anyway, this works.

What still confuses me about this language is that I'd like to declare a global type. I go into MAIN and put

TYPE ERROR_CODES:
(NO_ERROR, ERROR_1, ERROR_2);
END_TYPE

but I get this crazy compiler error:
ERROR 3780: MAIN(4): 'VAR', 'VAR_INPUT', 'VAR_OUTPUT' or 'VAR_IN_OUT' expected

I mean, it just makes sense to declare types before declaring variables, n'est-ce pas?

 

Click on the Data Types tab in the left pane of the editor, then define your structures, enums and aliases by right clicking and selecting Create Object

Actions are a bit like methods, but (unfortunately) they do not return a value, so you have to use an output variable of the fb. Bit clumsy, but it works. Roll on TwinCAT 3!

Roger