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Look at the curly-brace dereferencing again. As in the earlier
example, the array reference for Gilligan's provision list is ${$all_with_names[2]}[1].
Now, what if you want to know Gilligan's first provision? You need to dereference
this item one more level, so it's Yet Another Layer
of Braces: ${${$all_with_names[2]}[1]}[0]. That's
a really noisy piece of syntax. Can you shorten that? Yes!
Everywhere you write ${DUMMY}[$y],
you can write DUMMY->[$y] instead. In other
words, you can dereference an array reference, picking out a particular element
of that array by simply following the expression defining the array reference
with an arrow and a square-bracketed subscript.
For this example, this means you can pick out the array reference
for Gilligan with a simple $all_with_names[2]->[1],
and Gilligan's first provision with $all_with_names[2]->[1]->[0].
Wow, that's definitely easier on the eyes.
If that wasn't already simple enough,
there's one more rule: if the arrow ends up between "subscripty kinds of
things," like square brackets, you can also drop the arrow. $all_with_names[2]->[1]->[0]
becomes $all_with_names[2][1][0]. Now it's looking
even easier on the eye.
The arrow has to be between subscripty
things. Why wouldn't it be between? Well, imagine a reference to the array @all_with_names:
my $root = \@all_with_names;
Now how do you get to Gilligan's first item?
$root -> [2] -> [1] -> [0]
More simply, using the "drop arrow" rule, you can use:
$root -> [2][1][0]
You cannot drop the first arrow, however, because that would mean
an array @root's third element, an entirely unrelated
data structure. Let's compare this to the full curly-brace form again:
${${${$root}[2]}[1]}[0]
It looks much better with the arrow. Note, however, that no shortcut gets the entire array from an array reference. If you want all of Gilligan's provisions, you say:
@{$root->[2][1]}
Reading this from the inside out, you can think of it like this:
$root.
The last step doesn't have a shortcut arrow form. Oh well.[4]
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Created: March 27 2003
Revised: July 15, 2003
URL: http://webreference.com/programming/perl/learning/chap3/1
