Re: my @ARGV

[ikegami]

So does my $_; and my $var;. Is there a case where my doesn't create a new variable?

[ysth]

my $_ is new with 5.10.0, and switches anything in the scope that by default is using the global $_ to using the lexical $_ instead.

my @ARGV has no such magic. readline or eof will continue to default to using the global @ARGV, even though there's a lexical @ARGV in scope. This is the reason for a warning.

[szabgab]

My point is that I am looking for cases of Perl code that compile under use strict. Don't generate warnings under use warnings but don't do the expected by a beginner.

After being told to use strict and declare everything with my, a beginner will go out and do just that. Declare everything with my:

my (@ARGV, $a, $b, $_, $AUTOLOAD);

you could give them a list of special cases but IMHO it is a waste of brain cycles - at that point in the learning curve. Probably they will not learn them and the whole thing will just confuse them.

My plan is to provide a tool that can find such cases and warn about them.

[SuicideJunkie]

After being told to use strict and declare everything with my, a beginner will go out and do just that. Declare everything with my

Rather than telling them to 'declare everything with my', it would be more correct to simply say 'declare all of your variables'.
Then provide an example, such as:

It reminds me of pre-school; my $lollypop is all MINE! Nobody else can decrement it.
I'm sharing my blocks, so they are really our @blocks; now. Everybody in the room can push and shift them.
And my friend Perl is sharing his @ARGV with me. Look; he put a '-help' behind the first door, how cute.

The point being that variables, like toys, only need to be created once. The people you are sharing with don't need to buy/declare it, because you did that already.
Ownership and sharing are things we learned in kindergarten (hopefully!). Once the connection is made, it should be pretty natural.

[ysth]

Maybe you could provide integration (unless you already do - haven't kept up, but hope to after upgrading to ubuntu 8.10) with B::Lint and/or Perl::Critic?