4.2. What if That Was the Name?Typically, all references to a variable are removed 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 the @skipper array is declared, you have one reference to the five-element list. After $ref is initialized, you'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 not removed from memory, and $ref is still pointing to that data. At this point, the five-element list is contained within an anonymous array, which is a fancy term for an array without a name. Until the value of $ref is changed, or $ref itself disappears, you can still continue to use all the dereferencing strategies you used prior to when the name of the array disappeared. In fact, it's still a fully functional array that you can shrink or grow just as you do any other Perl array: push @$ref, "sextant"; # add a new provision print "$ref->[-1]\n"; # prints sextant\n You can even increase the reference count at this point: my $copy_of_ref = $ref; or equivalently: my $copy_of_ref = \@$ref; The data remains alive until the last reference is destroyed: $ref = undef; # not yet... $copy_of_ref = undef; # poof! Copyright © 2003 O'Reilly & Associates. All rights reserved. |
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