Function or Global Variable for ThisDrawing

I am trying to take my lisp programming up a notch (ba BAM! , and I am
looking for some input on some techneques.

Currently I have a function defined for ThisDrawing access, which looks like
this
(defun SM:ThisDwg (/) (vla-get-activeDocument (vlax-get-acad-object)))

Whenever I need to reference ThisDrawing I do it by calling the function.
However, it occurs to me that a better method might be to define a global
variable and set it using s::startup. This way, I only actually access the
object the once, and then access the value in the variable from then on.
However, I have some questions about this approach...
1: does each drawing get its own variable space, such that a global variable
would work with multiple drawings open, with the same named variable in each
drawing pointing to a different ThisDrawing?
2: this approach requires spreading my code into s::startup, while the
function call leaves all my code more self contained. Is the performance hit
for using the function call so small as to make it not an issue, and keeping
things together is better?
3: If the global variable works for ThisDrawing, can you also create a
global variable available from every drawing that is set in Acaddoc.lsp to
the Acad object?

Lastly, I have seen suggestions to put (vl-load-com) in every routine that
needs access. If I know that much of my code needs it, could I not just put
one (vl-load-com) in Acaddoc.lsp and be assured that every VL routine would
be fine?

Thanks for the help,
Gordon

 

Lastly, I have seen suggestions to put (vl-load-com) in every routine that

Gordon, I'll leave the fancy stuff for the braniacs -- you're over my head,
and I'm just curious as to where you're heading with all this.

But on the (vl-load-com), I run it only once in my acad.lsp and don't need
to run it in each document or application. If I were doing a standalone lisp
that needed to run outside the context of my customizations, then I would
include it in that lisp.

 

(defun ThisDrawing ()
(defun ThisDrawing ()
*ThisDrawing*
)
(setq *ThisDrawing* (vla-get-ActiveDocument (vlax-get-acad-object)))
)

 

OK Tony, you lost me there. Why the two defuns? And is this a function that
is only run once? If so, could it be outside a defun, and inside s::startup
so as to run each time a drawing is opened or created?

Best,
Gordon

 

The intent may be obscured there. It is similar to this, without the
conditional test:

(defun ThisDrawing ()
(cond (*ThisDrawing*)
((setq *ThisDrawing* (vla-Get-ActiveDocument
(vlax-Get-Acad-Object))))))


--
R. Robert Bell

OK Tony, you lost me there. Why the two defuns? And is this a function that
is only run once? If so, could it be outside a defun, and inside s::startup
so as to run each time a drawing is opened or created?

Best,
Gordon

 

Ah, so you use a function, and the function only actually goes to the
ThisDrawing object if the global variable doesn't yet exist, otherwise it
returns the value of the variable. If I remember right a VL function returns
the value of the last SETQ, so you don't need to do the VBA version of
FunctionName = GlobalVariable to end the funtion, correct?

By the way, Robert, what happened to that web site you used to be involved
with? I remember downloading your AU/AUGI error trap class some time ago,
along with seeing all sorts of great code examples. Now I can't find the
site.

Best,
Gordon

 

Gordon,
The first time the function is called it
1) redefines itself so that the next time it is called,
it will just return the global value.
2) sets up the global.

After the first call, the function is reduced to
(defun ThisDrawing () *ThisDrawing*)

 

In contradiction to what Robert suggests, the intent is clear
provided you understand the concept, mainly how a function
can redefine itself the first time it is called, so that it does
something differently in subsequent calls.

 

Like "autoload".

 

Thanks everyone. I knew I was going to learn something unexpected. I didn't
realize you could redefine a defun. Cool.

Best,
Gordon

 

I didn't realize you could redefine a defun. Cool.

Sure, like James said, that's how autoload works, it creates a defun on the
fly that redefines itself first time it runs. Diabolically clever.

 

We took the site down for a while, and haven't had the time to get a new
host to get it back up. Some day... ;^)

--
R. Robert Bell

Ah, so you use a function, and the function only actually goes to the
ThisDrawing object if the global variable doesn't yet exist, otherwise it
returns the value of the variable. If I remember right a VL function returns
the value of the last SETQ, so you don't need to do the VBA version of
FunctionName = GlobalVariable to end the funtion, correct?

By the way, Robert, what happened to that web site you used to be involved
with? I remember downloading your AU/AUGI error trap class some time ago,
along with seeing all sorts of great code examples. Now I can't find the
site.

Best,
Gordon