Setting a variable equal to a reference

babel17 has asked for the wisdom of the Perl Monks concerning the following question:

If I set a variable equal to a reference, is the reference count of the item pointed to by the reference incremented?

I am going to show an example that's slightly more complicated than necessary cause it better represents what I'm trying to accomplish.

my $foo = {
    by_id    => {
        0    => {
            id    => 0,
            name    => "bob",
            other    => "Nothing to see here",
        },
    },
};

$foo->{by_name}{bob} = $foo->{by_id}{0};
[download]

If I delete $foo->{by_id}{0};, is $foo->{by_name}{bob} still valid?

It's quite easy to simply test this, but I'm more interested in the discussion I hope to provoke in order to better understand perl's internal plumbing.

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Re: Setting a variable equal to a reference by ikegami (Patriarch) on Jul 31, 2013 at 02:03 UTC
`delete $foo->{by_id}{0}` deletes an element of the hash `%{ $foo->{by_id} }`. The value of that element is a ref. That ref is not referenced by anything else, so it will be freed. The referenced hash is is referenced by something else (the ref in `$foo->{by_name}{bob}`), so it won't be freed. So, Nothing touches the hash `%{ $foo->{by_name} }`. Nothing touches the ref in `$foo->{by_name}{bob}` (a copy of the ref that was in `$foo->{by_id}{0}`). The hash referenced by `$foo->{by_name}{bob}` is not freed.	[reply] [d/l] [select]
Re: Setting a variable equal to a reference by zork42 (Monk) on Jul 31, 2013 at 04:34 UTC
I'm more interested in the discussion I hope to provoke in order to better understand perl's internal plumbing. Devel::Peek might be of interest. It lets you examine the reference count and other internal properties of scalars and other data types. It refers to perlguts Also, try index-internals	[reply]
Re: Setting a variable equal to a reference (tryitstosee) by Anonymous Monk on Jul 30, 2013 at 22:39 UTC
It's quite easy to simply test this, but I'm more interested in the discussion I hope to provoke in order to better understand perl's internal plumbing. If you want to provoke a discussion, ask something different, otherwise, try it to see, because that's all there is to it	[reply]