Re^2: dereferencing a double array

Thank you very much for the elaborate reply. As you noted in your reply, the subroutines do return a new, completely different array. In that case, you mentioned: "the values have to be copied one way or another. I'd write it different though:

sub foo {
        my $array = shift;
        my $copy  = [map {[@$_]} @$array];
        ... Changes in $copy won't affect $array ...
        return $copy;
    }
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As i can see, now $copy is a reference that points to an array of (a new set of) references, each of which contain the same elements as the corresponding reference in @original_array. It could be written in this way though.

sub foo {
        my $array = shift;
        my @copy  = map {[@$_]} @$array;
        ... Changes in @copy won't affect @array ...
        return \@copy;
    }
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right? And is the reason that you'd copy the elements this way is that it's faster? Again, thanks a lot for your tips, Hadi

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Re^3: dereferencing a double array by JavaFan (Canon) on Oct 16, 2008 at 21:22 UTC
Yes, you can write it with @copy and returning it as \@copy. But I prefer using $copy, for symmetrical reasons. I start out with a reference to an array, so if I copy it, I'd like to copy to another reference. But that's just personal preference, I don't one way is significantly faster or easier to understand than the other. As for copying using a map instead of the double loop is mostly because it's less verbose. It's just one line and I see immediately it's a copy of a 2D array - the double loop takes more lines, and too large to immediately see what it does. I haven't benchmarked it, but if there's a difference I expect the difference to be small, and the map to be slightly faster; with the difference slowly growing if the arrays get larger. But speed isn't my main reason to copy it using a map.	[reply]
Re^4: dereferencing a double array by perlrocks (Acolyte) on Oct 16, 2008 at 21:31 UTC
Oh i see. What if efficiency and running time are of the utmost importance? Any tips? :) Thanks	[reply]
Re^5: dereferencing a double array by JavaFan (Canon) on Oct 16, 2008 at 22:08 UTC
What if efficiency and running time are of the utmost importance? Then your choice of Perl as a programming language is a horrible mistake.	[reply]