Jacob Chapa wrote:
> what is the difference between
>
> ->
That is the Perl dereferencing operator. You use it to access hash or array
elements, or package [class] methods, from a reference.
my $keywords_ref = {};
$keywords_ref->{Animal} = 'Movement';
$keywords_ref->{Vegetable} = 'Photosynthesis';
$keywords_ref->{Mineral} = 'Chrystallization';
> and
>
> =>
... is the key-value pairing operator. It is used in static initiaors for Perl
hashes, and can be very helpful in aligning keys and values to make group
assgnments visually clear:
my $keywords_ref = {
Animal => 'Movement',
Vegetable => 'Photosynthesis',
Mineral => 'Chrystallization',
'Sentient being' => 'Don\'t look at me. I\'m just a human'
};
Which offers a reference to an anonymous hash initiated with the pairs
indicated.
Hashes declared directly can also be populated using this operator:
my %keywords= (
Animal => 'Movement',
Vegetable => 'Photosynthesis',
Mineral => 'Chrystallization',
'Sentient being' => 'Don\'t look at me. I\'m just a human'
);
Note that parenthese are used in this context
and the arrow operator can be used with references to hashes declared either way
my $keywords_ref = \%keywords;
$keywords_ref->{'Protistan'} = 'One-celled';
which can be very useful when using the hash or other struture in a function.
In fact it is necessary if you wish to midify the values of the original
structure from within the function:
print_key_words($keywords_ref );
print "$_: $keywords{$_}\n" foreach keys %keywords;
sub print_key_words {
my $keywords_ref = shift;
print "$_: $keywords_ref->{$_}\n" foreach keys %$keywords_ref;
$keywords_ref->{$_} .= '--has been printed once' foreach keys %$keywords_ref;
}
If you put that all together, you can get an idea of how each of these operators
does its work:
Greetings! C:\Documents and Settings\rjnewton>perl -w
my %keywords = (
Animal => 'Movement',
Vegetable => 'Photosynthesis',
Mineral => 'Chrystallization',
'Sentient being' => 'Don\'t look at me. I\'m just a human'
);
my $keywords_ref = \%keywords;
$keywords_ref->{'Protistan'} = 'One-celled';
print_key_words($keywords_ref );
print "$_: $keywords{$_}\n" foreach keys %keywords;
sub print_key_words {
my $keywords_ref = shift;
print "$_: $keywords_ref->{$_}\n" foreach keys %$keywords_ref;
$keywords_ref->{$_} .= '--has been printed once' foreach keys %$keywords_ref;
}
Joseph
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