Re: variables: open issue a) date variables

On Saturday 03 May 2003 17:08, ned(_dot_)freed(_at_)mrochek(_dot_)com wrote:
<snip>
> I do note, however, that nobody
> else is jumping in to support this prefix idea. I'm ambivalent about
> it myself.
<snip>

It's weekend ;-)

As we _have_ magic variables in the current draft (year, month, etc) 
that are implicitly changed by commands (as opposed to be set with 
"set"), no matter if we call them thus or not, it would be a good idea 
to make that explicit and to enable other extensions to define their 
own magic/system variables.

The reasons against magic/system variables Kjetil mentioned were:

1. Year, month, etc. are not really magic, you can write them via set
   and they only spring into life on setdate.

I think we agree that writing to those variables is not a good idea, 
since it's not needed, makes program flow analysis more complex and 
produces potentially invalid system variable content that leads to a 
new class of runtime errors not present with read-only system 
variables.

Furthermore, that they spring into life as a side-effect of a command is 
proof, not disproof, of their magicness.

2. There's no good use for them.

Well, the fact that they are being defined (whether called system 
variables or not) in itself is proof of their usefulness. imapflags 
could also make good use of system variables. In fact, IIRC, the 
imapflags extension was was what prompted the variables extension in 
the first place.

3. We'd need a registry for them, since extensions could conflict.

They can still conflict if we don't make system variables explicit in 
the variables extension. Prefixing them at least avoids conflicts with 
user variables.

As to requiring a registry. Sure, that would be nice, but isn't a 
necessity. We don't have a registry for command or test identifiers 
either, even though they could also conflict between extensions. 
Instead, we believe the extension authors and the review process to 
avoid these conflicts.

Marc

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