On 16 May 2000 11:06:13 -0400, [EMAIL PROTECTED] (David S. Rosinger)
wrote:
>Jan, this is leading me into some questions on style. Let's take the
>following for example from build 522:
>
> d:/Perl/bin/ppm.pl
Please don't use the ppm source code as a base for stylistic wisdom; some
of the code in there is still from the days when the author was learning
Perl.
>The following lexical variable has *file scope*:
>
> my %options = PPM::GetPPMOptions();
>
>Then several variables are made *global*:
>
> use vars qw ($location $Ignorecase $clean
> $confirm $force_install $root $build_dir $more
> $trace $tracefile $verbose);
>
>and set with *typeglob* notation:
>
> *Ignorecase = \$options{'IGNORECASE'};
>
>Question #1: What is the point of using a typeglob here?
This is aliasing $Ignorecase and $options{IGNORECASE}. They now point to
the same variable; changing one will also change the other (because they
are the same).
>And from:
>
> What's New in Perl 5.6.0?
>
> http://www.perl.com/pub/2000/04/whatsnew.html
>
> | `our' Variables
> |
> | Whereas `my' declares lexical variables, `our' declares global
> | variables - it's a cleaner and hopefully more intuitive
> | replacement for `use vars'.
>
>Question #2: Is `our' merely syntactic sugar, or does it change the
>behavior of global variables in some way? Does it behave differently
>at compile time than `use vars'?
"our" is lexically scoped:
if ($cond) {
our $var = 42;
}
print $var; # will create an error under "use strict"
The "use vars" stuff is visible throughout the rest of the compilation
unit. With "our" you can define dynamic variables just within a lexical
scope (yes, a confusing concept; you have to differentiate between
lexical visibility and dynamic lifetime).
Another property to watch out for is that "our" works across package
"boundaries", just like "my":
package Foo;
our $x = 42;
print $x; # prints $Foo::x
package Bar;
print $x; # still prints $Foo::x
our $x;
print $x; # now prints $Bar::x
-Jan
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