Re: Readonly references, replicating data structures

[haukex]

Hi nikmit,

I expected the below code to create a fresh copy of @arr every time gimme() is executed.

In the code you showed, @arr is only initialized once, so the anonymous hashes are only created once. The first and only element of @arr is a reference to an anonymous hash. When you say my @result = @arr;, the elements of @arr are copied into @result, so that reference is copied exactly, so it still points to the same anonymous hash. This is known as a "shallow copy" and is how arrays and hashes are copied in Perl. (Note: Making @arr Readonly won't change that.)

To get a "deep copy" or "clone", choroba already pointed you to Storable and Clone, but there's another solution:

sub gimme {
    my @result = ( {
        box => { attr => 'foo' },
        } );
    return \@result;
}

This causes the array and the anonymous hashes to be re-created on every call to gimme.

Hope this helps,
-- Hauke D

Update: Minor clarifications to wording.