Section 5.2. What If That Was the Name?


5.2. What If That Was the Name?

Typically, all references to a variable are gone before the variable itself. But what if one of the references outlives the variable name? For example, consider this code:

 my $ref; {   my @skipper = qw(blue_shirt hat jacket preserver sunscreen);   $ref        = \@skipper;   print "$ref->[2]\n"; # prints jacket\n } print "$ref->[2]\n"; # still prints jacket\n 

Immediately after we declare the @skipper array, we have one reference to the five-element list. After $ref is initialized, we'll have two, down to the end of the block. When the block ends, the @skipper name disappears. However, this was only one of the two ways to access the data! Thus, the five-element list is still in memory, and $ref still points to that data.

At this point, the five-element list is in an anonymous array, which is a fancy term for an array without a name.

Until the value of $ref changes, or $ref itself disappears, we can still use all the dereferencing strategies we used prior to when the name of the array disappeared. In fact, it's still a fully functional array that we can shrink or grow just as we do any other Perl array:

 push @$ref, 'sextant'; # add a new provision print "$ref->[-1]\n"; # prints sextant\n 

We can even increase the reference count at this point:

 my $copy_of_ref = $ref; 

or equivalently:

 my $copy_of_ref = \@$ref; 

The data stays alive until we destroy the last reference:

 $ref = undef; # not yet... $copy_of_ref = undef; # poof! 




Intermediate Perl
Intermediate Perl
ISBN: 0596102062
EAN: 2147483647
Year: N/A
Pages: 238

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