roboticus:

I think the reason that the destroy method executes after print completes is because a reference to the object is placed on the stack, and the reference count goes to zero when the parameters are cleared from the stack.

So the idea is that DESTROY is called immediately when the reference count falls to zero, but that the decrementing of the reference count does not occur immediately upon the call to undef? That sounds reasonable, but I’m not sure which stack is meant. It can’t be the subroutine’s parameter list:

#! perl
use strict;
use warnings;

{
    package Foo;

    sub new
    {
        return bless {};
    }

    sub DESTROY
    {
        print "Foo::DESTROY\n";
    }
}

my  $foo = Foo->new();
bar($foo);
print "Back in main\n";

sub bar
{
    print "Begin bar()\n";
    undef $_[0];
    print "End bar()\n";
}
[download]

Output:

 3:14 >perl 556_SoPW.pl
Begin bar()
Foo::DESTROY
End bar()
Back in main

 3:18 >
[download]

Can you clarify what you mean by “a reference to the object is placed on the stack”?

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