in reply to Re^2: Debugger and lexicals
in thread Debugger and lexicals

Some of what you say I can agree with. But "they only exist within a lexical scope"---and why's that? It's because lexical variables cannot access the symbol table. That's why I mentioned that there's a control "sandboxed" way from the debugger. Package variables can be accessed via the symbol table.

As for my $a getting optimized away, I disagree with that because I just don't see how it can be optimized away when it's uninitialized in the subroutine. Here's a little test that I ran: 

#!/usr/bin/perl

use strict;
use warnings;

print mt2(55), "\n";

my $a = 23;

sub mt2 { 
    my $b = $_[0] * 2;
    return $a + $b;
}

[download]
Here's the corrected script: 

#!/usr/bin/perl

use strict;
use warnings;

print mt2(55), "\n";

sub mt2 { 
    my $a = 23;
    my $b = $_[0] * 2;
    return $a + $b;
}

[download]
This one works in the debugger. Thanks for the input.

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Re^4: Debugger and lexicals
by Anonymous Monk on Aug 07, 2011 at 11:59 UTC

    and why's that? It's because lexical variables cannot access the symbol table.

    No, its because they're initialized at runtime and stored in a pad/Scratchpads, which are attached to subroutines ... http://search.cpan.org/dist/illguts/

    As for my $a getting optimized away, I disagree with that because I just don't see how it can be optimized away when it's uninitialized in the subroutine. Here's a little test that I ran:

    Your example is different.

    In your example, $a is initialized after the call to mt2.

    And you never remove a reference to $a, so it never gets optimized away.

    Here is what you intended :)

    $a is defined
    Read more... (378 Bytes)
    Read more... (887 Bytes)
    The "problem" of $a being undefined, is because it is optimized away -- really because the sub which we're stepping into (ASDF) doesn't refer to it
    Read more... (361 Bytes)
    Read more... (825 Bytes)

    Here, a different sub refers to $a, so when we step into ASDF, $a is still undefined -- it is not attached to ASDF's Scratchpad
    Read more... (395 Bytes)
    Read more... (825 Bytes)

    You should consider not answering or prefacing your guesses (see To Answer, Or Not To Answer....), because there won't always be someone there to answer when Duty Calls

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[d/l]
[select]
      Stricly speaking $a is not optimised away; it just has a short life span, as as I pointed out earlier. 
      $ cat /tmp/Foo.pm 
package Foo;
sub DESTROY { print "DESTROY\n" }
my $a = bless {};
print "executing Foo\n";

$ perl -I/tmp -e'use Foo; BEGIN { print "BEGIN\n" }'
executing Foo
DESTROY
BEGIN

      [download]

      Dave.

[reply]
[d/l]

        Stricly speaking $a is not optimised away; it just has a short life span, as as I pointed out earlier.

        Yeah, because it isn't attached to any scratchpad

[reply]

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