-=head1 TITLE
+=head1 NAME
perlLoL - Manipulating Lists of Lists in Perl
-=head1 Declaration and Access
+=head1 DESCRIPTION
+
+=head1 Declaration and Access of Lists of Lists
The simplest thing to build is a list of lists (sometimes called an array
of arrays). It's reasonably easy to understand, and almost everything
structures.
A list of lists, or an array of an array if you would, is just a regular
-old array @LoL that you can get at with two subscripts, like $LoL[3][2]. Here's
+old array @LoL that you can get at with two subscripts, like C<$LoL[3][2]>. Here's
a declaration of the array:
# assign to our array a list of list references
Notice that the outer bracket type has changed, and so our access syntax
has also changed. That's because unlike C, in perl you can't freely
interchange arrays and references thereto. $ref_to_LoL is a reference to an
-array, whereas @LoL is an array proper. Likewise, $LoL[2] is not an
+array, whereas @LoL is an array proper. Likewise, C<$LoL[2]> is not an
array, but an array ref. So how come you can write these:
$LoL[2][2]
$ref_to_LoL->[2]->[2]
Well, that's because the rule is that on adjacent brackets only (whether
-square or curly), you are free to omit the pointer dereferencing array.
-But you need not do so for the very first one if it's a scalar containing
+square or curly), you are free to omit the pointer dereferencing arrow.
+But you cannot do so for the very first one if it's a scalar containing
a reference, which means that $ref_to_LoL always needs it.
=head1 Growing Your Own
if you knew where you wanted to put it:
my (@LoL, $i, $line);
- for $i ( 0 .. 10 )
+ for $i ( 0 .. 10 ) {
$line = <>;
$LoL[$i] = [ split ' ', $line ];
}
or even just
my (@LoL, $i);
- for $i ( 0 .. 10 )
+ for $i ( 0 .. 10 ) {
$LoL[$i] = [ split ' ', <> ];
}
-You should in general be leary of using potential list functions
+You should in general be leery of using potential list functions
in a scalar context without explicitly stating such.
This would be clearer to the casual reader:
my (@LoL, $i);
- for $i ( 0 .. 10 )
+ for $i ( 0 .. 10 ) {
$LoL[$i] = [ split ' ', scalar(<>) ];
}
=head1 Slices
-If you want to get at a slide (part of a row) in a multidimensional
+If you want to get at a slice (part of a row) in a multidimensional
array, you're going to have to do some fancy subscripting. That's
because while we have a nice synonym for single elements via the
pointer arrow for dereferencing, no such convenience exists for slices.
}
-=head1 Passing Arguments
-
-One place where a list of lists crops up is when you pass
-in several list references to a function. Consider:
-
- @tailings = popmany ( \@a, \@b, \@c, \@d );
-
- sub popmany {
- my $aref;
- my @retlist = ();
- foreach $aref ( @_ ) {
- push @retlist, pop @$aref;
- }
- return @retlist;
- }
-
-This function was designed to pop off the last element from each of
-its arguments and return those in a list. In this function,
-you can think of @_ as a list of lists.
-
-Just as a side note, what happens if the function is called with the
-"wrong" types of arguments? Normally nothing, but in the case of
-references, we can be a bit pickier. This isn't detectable at
-compile-time (yet--Larry does have a prototype prototype in the works for
-5.002), but you could check it at run time using the ref() function.
-
- use Carp;
- for $i ( 0 .. $#_) {
- if (ref($_[$i]) ne 'ARRAY') {
- confess "popmany: arg $i not an array reference\n";
- }
- }
-
-However, that's not usually necessary unless you want to trap it. It's
-also dubious in that it would fail on a real array references blessed into
-its own class (an object). But since you're all going to be using
-C<strict refs>, it would raise an exception anyway even without the die.
-
-This will matter more to you later on when you start building up
-more complex data structures that all aren't woven of the same
-cloth, so to speak.
-
=head1 SEE ALSO
perldata(1), perlref(1), perldsc(1)
=head1 AUTHOR
-Tom Christiansen <tchrist@perl.com>
+Tom Christiansen E<lt>F<tchrist@perl.com>E<gt>
Last udpate: Sat Oct 7 19:35:26 MDT 1995
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