FAQ 7.14 What is variable suicide and how can I prevent it?



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7.14: What is variable suicide and how can I prevent it?

This problem was fixed in perl 5.004_05, so preventing it means
upgrading your version of perl. ;)

Variable suicide is when you (temporarily or permanently) lose the value
of a variable. It is caused by scoping through my() and local()
interacting with either closures or aliased foreach() iterator variables
and subroutine arguments. It used to be easy to inadvertently lose a
variable's value this way, but now it's much harder. Take this code:

my $f = 'foo';
sub T {
while ($i++ < 3) { my $f = $f; $f .= "bar"; print $f, "\n" }
}

T;
print "Finally $f\n";

If you are experiencing variable suicide, that "my $f" in the subroutine
doesn't pick up a fresh copy of the $f whose value is <foo>. The output
shows that inside the subroutine the value of $f leaks through when it
shouldn't, as in this output:

foobar
foobarbar
foobarbarbar
Finally foo

The $f that has "bar" added to it three times should be a new $f "my $f"
should create a new lexical variable each time through the loop. The
expected output is:

foobar
foobar
foobar
Finally foo



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