Re: Help with references

I wont reiterate the importance of 'strict' and 'warnings' ... (it is very useful) instead, I'm gonna tell you what you won't hear from anyone else.

I post this because you said this is your first programming language. Others will disagree with what I am about to tell you, and this may seem like weird advice, but you can judge for yourself. ... Disclaimer: extremely biased opinion follows ... IMHO the single best way to 'wrap your brain' around working with references is to absolutely avoid using the 'backslash notation' whenever possible, and just treat everything as a scalar. This may take a moment to sink in, but let me explain, and consider this example ...

### re-worked version of your original code

my $ref1 = [(0..9)];      ### start with anon array refs
my $ref2 = [('a'..'l')];  ### from the very beginning

my ($aOne, $aTwo) = &f($ref1, $ref2);
print '@a1 is:  '. "@{$aOne}\n";
print '@a2 is:  '. "@{$aTwo}\n";

sub f {
    my $a1 = shift || die 'Hey! I expected an array ref ';
    my $a2 = shift || die 'expected array ref here too ';

    ### do something, for example ...
    @{$a2} = reverse @{$a2};

    return ($a1, $a2);
}

__END__
@a1 is:  0 1 2 3 4 5 6 7 8 9
@a2 is:  l k j i h g f e d c b a
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rationale

the little 'backslash notation' just sucks. It is ugly, it is error prone, it is confusion-inducing, and it is one of the worst widespread typographical conventions in the entire field of computer programming. Avoid using it with your variables. (aside from stuff like \n, which is basically a constant) Your brain will thank you for it.
just think to yourself "scalars can hold *anything*", not just strings ... then you realize the hardest part is just picking a variable name (eg $ref1, $aryRef1, $hashRef1, $bigHugeNestedVariable1, etc) to remind you of what that scalar is expected to be holding
suppose you want to change your arrays to hashes or something else? It's a PITA to go around changing all those little \@ symbols to \% symbols, and much clearer to change 'die expected array ref' to 'die expected hash ref'. Either way, you will have to change the code, but one set of changes is easier on the cognitive process than the other. You can decide for yourself which ones.

Just remember: 1) "scalars can hold anything" (the variables with the dollar sign in front) use them; 2) give those scalars a good name to reflect what's expected of them; and 3)properly 'morph' those scalars into proper versions of what they are holding with @{$foo}, @$foo, %{$foo}, or %$foo, notation .. or $foo->(), $foo->{baz}{blee}{blaa}( or whatever else is appropriate ) and you're done.

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Re^2: Help with references by beable (Friar) on Jul 02, 2004 at 02:24 UTC
I agree that it's easier to use references throughout your program, rather than having to deal with real arrays and references to arrays. The same applies to hashes. One other thing is that you can use the arrow operator to index into the array refererence with square brackets, as the example below demonstrates. You can do a similar thing with hash references. #!/usr/bin/perl use strict; use warnings; run(); sub run { my $arr1 = [0 .. 12]; my $arr2 = ['a' .. 'l']; print "before:\n"; print "arr1 = @{$arr1}\n"; print "arr2 = @{$arr2}\n"; # because we're passing references to arrays, any changes # made to the arrays in the subroutine will affect the arrays # here as well. No need to return the arrays. f($arr1, $arr2); # use the arrow operator and square brackets to index the # array, same as in the subroutine below - same syntax, # less confusing $arr1->[7] = "SEVEN!"; print "after:\n"; print "arr1 = @{$arr1}\n"; print "arr2 = @{$arr2}\n"; } sub f { my ($arr1, $arr2) = @_; for (my $i = 0; $i < 5; $i++) { # shuffle some stuff around my $index1 = rand($#$arr1); my $index2 = rand($#$arr2); # use the arrow operator and square brackets to index # the array through a reference my $tmp = $arr1->[$index1]; $arr1->[$index1] = $arr2->[$index2]; $arr2->[$index2] = $tmp; } } [download]	[reply] [d/l]

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Re^2: Help with references
by beable (Friar) on Jul 02, 2004 at 02:24 UTC

#!/usr/bin/perl

use strict;
use warnings;

run();

sub run
{
    my $arr1 = [0 .. 12];
    my $arr2 = ['a' .. 'l'];

    print "before:\n";
    print "arr1 = @{$arr1}\n";
    print "arr2 = @{$arr2}\n";

    # because we're passing references to arrays, any changes
    # made to the arrays in the subroutine will affect the arrays
    # here as well. No need to return the arrays.
    f($arr1, $arr2);

    # use the arrow operator and square brackets to index the
    # array, same as in the subroutine below - same syntax,
    # less confusing
    $arr1->[7] = "SEVEN!";

    print "after:\n";
    print "arr1 = @{$arr1}\n";
    print "arr2 = @{$arr2}\n";
}

sub f
{
    my ($arr1, $arr2) = @_;

    for (my $i = 0; $i < 5; $i++)
    {
        # shuffle some stuff around
        my $index1 = rand($#$arr1);
        my $index2 = rand($#$arr2);

        # use the arrow operator and square brackets to index
        # the array through a reference
        my $tmp = $arr1->[$index1];
        $arr1->[$index1] = $arr2->[$index2];
        $arr2->[$index2] = $tmp;
    }
}
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