So I'm stepping through some code in a cpan module ...

I have undef for @_, so I'm expecting to execute line 148 next. However, the debugger puts me on line 145. Why did it go to 145 instead of 148? Why would undef be treated as a true value? 

  DB<13> n
Net::DBus::RemoteService::get_object(/usr/lib/perl5/Net/DBus/RemoteSer
+vice.pm:144):
144:        if (@_) {
  DB<13> l
144==>        if (@_) {
145:        my $interface = shift;
146:        return $self->{objects}->{$object_path}->as_interface($int
+erface);
147         } else {
148:        return $self->{objects}->{$object_path};
149         }
150     }
151
152:    1;
153
  DB<13> x @_
0  undef
  DB<14> n
Net::DBus::RemoteService::get_object(/usr/lib/perl5/Net/DBus/RemoteSer
+vice.pm:145):
145:        my $interface = shift;
  DB<14> n
Net::DBus::RemoteService::get_object(/usr/lib/perl5/Net/DBus/RemoteSer
+vice.pm:146):
146:        return $self->{objects}->{$object_path}->as_interface($int
+erface);
  DB<14> x $interface
0  undef

[download]

The method was invoked as $proxy = $service->get_object($self->{object_path}, $mdata->{interface}); and the innards of the function have shifted the parameters into variables. So @_ should have 0 elements, right?

Here is the whole method from /usr/lib/perl5/Net/DBus/RemoteService.pm 
135     sub get_object {
136:        my $self = shift;
137:        my $object_path = shift;
138
139:        unless (defined $self->{objects}->{$object_path}) {
140:        $self->{objects}->{$object_path} = Net::DBus::RemoteObject
+->new($self,
141                                         $object_path);
142         }
143
144:        if (@_) {
145:        my $interface = shift;
146==>        return $self->{objects}->{$object_path}->as_interface($i
+nterface);
147         } else {
148:        return $self->{objects}->{$object_path};
149         }
150     }

[download]
Update: I just realized that the 1st parameter is the added class object. DUH :-( So it's a three element array. Back to this in a few after I rerun the debugger.

In reply to Two element array, shifted twice, is true? by SwaJime

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.