Re: [MacPerl] defining variables if not already defined

[Ronald J Kimball <rjk@linguist.dartmouth.edu>]

On Mon, Jul 24, 2000 at 07:45:08PM -0400, Paul Schinder wrote:
> At 4:14 PM -0700 7/24/00, Tom Sackett wrote:
> >The same thing happens no matter how I rewrite line 3, I've tried the
> >following:
> >   (my ($var) = "conga") unless (defined($var));
> >   my ($var) = "conga" if (!defined($var));
> >   (defined($var)) || (my ($var) = "conga");
> >
> >Any idea what's going on, or what I can do about it?
> 
> It *did* give you an warning message, didn't it?
> 
> # "my" variable $var masks earlier declaration in same scope.
> File 'Untitled'; Line 3
> The variable is: bongo
> The variable is now:
> 
> That's what's going on.  You're "my"ing a variable twice in the same 
> scope, which is A Bad Thing.

my has a compile time effect and a runtime effect, so in this code:

my($var) = "conga" unless (defined($var));

the compile-time effect of lexicalizing $var occurs, *regardless* of the
value of $var at runtime.

This is an "undocumented feature".  :)

So, don't put a statement modifier on my() unless you know what you're
doing.

Ronald

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