Debugger, use strict, use warnings

Coleoid has asked for the wisdom of the Perl Monks concerning the following question:

Perhaps this is in the docs somewhere, but I missed it. If it is, a reference to its location will be enough for me. I think others will probably still trip over it, though...

F:\>perl -v

This is perl, v5.6.0 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2000, Larry Wall

Binary build 623 provided by ActiveState Tool Corp.
...et c...
F:\>perl -de 0
Default die handler restored.

Loading DB routines from perl5db.pl version 1.07
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(-e:1):   0
  DB<1> use strict;

  DB<2> use warnings;

  DB<3> print undef;

  DB<4> print $x[undef];

  DB<5> q
[download]

Now, I know (through experimentation) that if I do:

perl -wde 0
[download]

...I've got the warnings. Why don't I get the results when I put the 'use' lines in the debugger? Is it a _good_ reason?

J.

Comment on Debugger, use strict, use warnings Select or Download Code

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Re: Debugger, use strict, use warnings by LD2 (Curate) on Apr 10, 2001 at 08:22 UTC
You may be interested in this past node ... use warnings vs. perl -w as well as checking this out... Perl Lexical Warnings	[reply]
(tye)Re: Debugger, use strict, use warnings by tye (Sage) on Apr 10, 2001 at 20:10 UTC
Now, I know (through experimentation) that if I do: `perl -wde 0` ...I've got the warnings. Then you didn't do enough experimenting. ;) `> perl -we "print 0+'abc'" Argument "abc" isn't numeric in addition (+) at -e line 1. 0 > perl -wde 0 DB<1> print 0+'abc' 0` [download] But then your example surprised me because I had assumed that the debugger never gave me warnings for code entered at the command prompt. So I experimented further and decided that you can get run-time warnings but not compile-time warnings for code entered at the debuger's command prompt. But back to your real question... The debuger runs your code using eval (how else?). So your example code ends up being closer to this: `eval "use strict;"; eval "use warnings;"; eval "print undef;"; eval 'print $x[undef];';` [download] and pragmas obey scope so it makes sense (to me, at least) that use warnings and use strict don't do much good in the above code. I was going to suggest that you make a file e.pm: `use strict; use warnings; 1` [download] so you could do: `perl -de 0 DB<1> use e; print $x[undef]` [download] but that doesn't do any good. But that reminds me! How do you make pragma magic creep up an extra level of scope? I know how to do this with modules that export symbols. Sometimes it'd be nice to do that with pragmas as well. - tye (but my friends call me "Tye")	[reply] [d/l] [select]
Re (tilly) 2: Debugger, use strict, use warnings by tilly (Archbishop) on Apr 10, 2001 at 20:52 UTC
Making pragma logic move up an extra level of scope is easiest done by using caller to get your caller's package name and then doing an eval which sets the package and then calls the pragma. There are various compilation/runtime timing issues you have to get straight of course. But that will work.	[reply]
(tye)Re2: Debugger, use strict, use warnings by tye (Sage) on Apr 10, 2001 at 21:26 UTC
I'd like to see an example. I believe that pragmas affect the scope that is one level up not on the package that is one level up so I don't see how your suggestion would do any good. - tye (but my friends call me "Tye")	[reply]
Re (tilly) 4: Debugger, use strict, use warnings by tilly (Archbishop) on Apr 10, 2001 at 22:16 UTC
(tye)Re3: Debugger, use strict, use warnings by tye (Sage) on Apr 10, 2001 at 22:55 UTC
Re: (tye) Debugger, use strict, use warnings by Coleoid (Sexton) on Apr 11, 2001 at 20:26 UTC
Coleoid wrote: Now, I know (through experimentation) that if I do: `perl -wde 0` ...I've got the warnings. tye wrote: Then you didn't do enough experimenting. ;) `> perl -we "print 0+'abc'" Argument "abc" isn't numeric in addition (+) at -e line 1. 0 > perl -wde 0 DB<1> print 0+'abc' 0` [download] Hmm. My experiments were assorted hijinks with undef: `>perl -wde 0 DB<1> print undef; Use of uninitialized value in print at (eval 5) [D:/Perl/lib/perl5db.p +l:1510] line 2, <IN> line 1.` [download] So this gives me another question: Why which where? Some warnings, some of the time? And here I thought I almost got it. Time to hit the docs again.	[reply] [d/l] [select]
(tye)Re4: Debugger, use strict, use warnings by tye (Sage) on Apr 11, 2001 at 20:54 UTC
As I already said "you can get run-time warnings but not compile-time warnings for code entered at the debuger's command prompt," which I think answers part of your question. And I doubt there are any docs that cover this. As for the "why", I assume that the debugger restores $^W in-line with the eval of your code via the equivalent of `eval "\$^W= $saved; $your_code"` (it actually restores quite a few things so the syntax isn't quite what I wrote) which means that $^W isn't restored until after that code is compiled. Patching the debugger to do `eval "BEGIN{$^W= saved} $your_code"` would correct that but you'll have to be careful to separate the things that need to be restored at compile time from the things that can't be restored from within the BEGIN block because the restoration would be ruined when you leave the scope of that block. Creating such a patch sounds like a reasonable project. Let me know if you run into problems. ;) - tye (but my friends call me "Tye")	[reply] [d/l] [select]