[CMake] 2D arrays

[Robert Dailey]

On Wed, Nov 30, 2011 at 7:18 PM, Michael Hertling <mhertling at online.de>wrote:

> On 11/30/2011 03:29 AM, Robert Dailey wrote:
> > I use macros so the _array2d_ variables fall through the scope of the
> macro
> > and are available in the next call to array2d_advance(). I could use
> > functions + properties but this solution works, I saw no need to use the
> > slightly more verbose global properties feature.
>
> What I've had in mind are functions and the PARENT_SCOPE option of SET().
>

This is a good idea, thanks.


> > What specific helper variables are you referring to? I would most likely
> > use more uniquely mangled local variables instead, but I figured the
> > preceeding underscore in front of each was sufficient. What would you
> > recommend here? I'd like to avoid a cleanup() method because it seems
> > unnecessary. If my local variables cause conflicts later, and if name
> > mangling isn't the idiomatic solution, I'd like to hear whatever idea you
> > have (that doesn't involve cleanup() if possible).
>
> Because you must preserve some variables between multiple function/macro
> invocations - i.e. you can't work with local variables only - one might
> like to have a mean to purge these variables when their job is done in
> order to not pollute the current scope more than necessary. Of course,
> it's not absolutely indispensable, but if a set of non-local variables
> is used just internally by a set of related functions, it is possibly
> worth a thought how to not have these variables hang around later on.
>

When you say "pollute the current scope", what specific issues are you
referring to? In my experience the biggest danger are naming conflicts,
which are silent issues and cause subtle symptoms that are hard to debug.
I've attempted to remedy this, as I said, by using name mangling... i.e.
prefix everything with _array2d_, which I'm pretty sure no one else will
ever use.

I respect the notion of a cleanup method. I will implement one but it
really is optional... whether you call it or not, in practice, the
differences will never be noticed since the names are unique enough. Now,
if keeping those variables lingering around cause performance issues or
memory issues in CMake, then that's a different discussion.

> What would this buy me? Typically I've avoided ARGN unless it is
> absolutely
> > necessary, but a variable in this case seems more direct. Can you explain
> > what benefits this has?
>
> AFAICS, you don't need the "width" parameter because it can be obtained
> as the length of "var_names". Thus, additionally specifying "width" is
> error-prone; e.g. (width,var_names)=(3,"fruit;animal") is inherently
> invalid.
>
> Using ARGN would allow the user to specify the array elements freely as
> separate arguments at the end of array2d_begin_loop(), without the need
> to pass them in as a semicolon-separated list in double quotes.


Oh, I didn't realize you eliminated the "width" parameter. That's actually
a very awesome idea. I misread your code sample and thought you still kept
'width' but simply moved the list of field names to the end. I wasn't sure
what that would provide me :)

Great ideas and I will implement these and re-post my code. Hopefully it
can be added to CMake later or become useful to other people.
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