What’s “this”?

As I’m sure many of you will know, when you’re working with object oriented languages like C++, JavaScript and VB , the compiler provides you with a keyword (e.g. ‘this’ or ‘Me’) that you can use as a reference to the specific instance of an object under which the code is currently executing.  This provides a neat and easy way to access details about the current context when responding to events and methods, and generally improves the clarity of the code.

However, a ‘this/Me’ construct is not something we’ve really had in OpenInsight, because when we write our event handling code the system explicitly passes the name of the current object as the first argument called “CtrlEntID”, so in our event scripts we can use that instead.  Obviously this works well enough, but over the years I’ve found some situations where it would be nice to go a little further:

  • In many of the OpenInsight training courses I’ve run, one of the most common questions I get asked from new students is: “what is the equivalent of ‘this’, or “where is the ‘Me’ keyword”?   Having some sort of “this/me” construct in Basic+ would make learning the system much easier for them, and the name “CtrlEntID” hardly seems slick!
  • With the trend away from using event scripts and moving code into commuter modules the name “CtrlEntID” is no longer enforced – it can be named anything the author of the commuter module wishes, leading to a possible loss of clarity (for example in my own commuter modules I always use the variable name “Object” in place of “CtrlEntID”, but that’s just my convention, and is something subsequent code maintainers must adopt).
  • As code becomes deeper and more nested passing the “CtrlEntID” variable to each subsequent procedure as an argument becomes more of a chore, and I’ve seen global variables used in place of this which can lead to code that is difficult to maintain.

Of course, we do have the “@Window” system variable, which contains the name of the parent WINDOW instance for the currently executing context, so we’re nearly there, but unfortunately that’s not the same as ‘this/Me’ unless you’re responding to a WINDOW event.

So, with the release of version 10.0.8 we’ve now gone the whole way and added a new system variable called:

@Self

When an event is triggered this variable contains the full name of the control instance under which the event code is executing, just like @Window contains the name of the parent WINDOW instance.

E.g:

// Using CtrlEntID
Name = Get_Property( CtrlEntID, "TEXT" )

// Using @Self
Name = Get_Property( @Self, "TEXT" )

We’ve also included two more system variable names as synonyms for @Self as well:

@This
@Me

You may use these in place of @Self if you’re more inclined to use names that are familiar from another language (@Self was chosen because it is already referenced in OpenInsight as a pseudo-variable name when defining QuickEvents).

Hopefully, moving forward, this small addition may help to maintain a cleaner code-base and make teaching new students a little easier.

 

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