Attached is my patch to perldsc.pod. This is an attempt to make the
code in perldsc.pod something like what we want all our code to look
like. We complain when people don't use strict, or use double quotes
when they aren't needed, when code isn't consistent. I've tried to
remedy these things in this document.
Please post changes in the form of patches. ;-)
Casey West
--
I'd rather listen to Newton than to Mundie. He may have been dead for
almost three hundred years, but despite that he stinks up the room
less.
-- Linus
--- perl-current.orig/pod/perldsc.pod Thu Sep 13 21:42:52 2001
+++ perl-current/pod/perldsc.pod Mon Sep 17 13:42:13 2001
@@ -18,11 +18,11 @@
may now write something like this and all of a sudden, you'd have a array
with three dimensions!
- for $x (1 .. 10) {
- for $y (1 .. 10) {
- for $z (1 .. 10) {
- $AoA[$x][$y][$z] =
- $x ** $y + $z;
+ my @AoA;
+ for my $x (1 .. 10) {
+ for my $y (1 .. 10) {
+ for my $z (1 .. 10) {
+ $AoA[$x][$y][$z] = $x ** $y + $z;
}
}
}
@@ -102,7 +102,11 @@
out your array in with a simple print() function, you'll get something
that doesn't look very nice, like this:
- @AoA = ( [2, 3], [4, 5, 7], [0] );
+ my @AoA = (
+ [2, 3, ],
+ [4, 5, 7],
+ [0, ],
+ );
print $AoA[1][2];
7
print @AoA;
@@ -123,79 +127,46 @@
repeatedly. Here's the case where you just get the count instead
of a nested array:
- for $i (1..10) {
- @array = somefunc($i);
- $AoA[$i] = @array; # WRONG!
+ my @AoA;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $AoA[$i] = @array; # WRONG!
}
That's just the simple case of assigning an array to a scalar and getting
its element count. If that's what you really and truly want, then you
might do well to consider being a tad more explicit about it, like this:
- for $i (1..10) {
- @array = somefunc($i);
- $counts[$i] = scalar @array;
+ my @counts;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $counts[$i] = scalar @array;
}
-Here's the case of taking a reference to the same memory location
-again and again:
+Here's the right way to do the reference C<@array>:
- for $i (1..10) {
- @array = somefunc($i);
- $AoA[$i] = \@array; # WRONG!
- }
-
-So, what's the big problem with that? It looks right, doesn't it?
-After all, I just told you that you need an array of references, so by
-golly, you've made me one!
-
-Unfortunately, while this is true, it's still broken. All the references
-in @AoA refer to the I<very same place>, and they will therefore all hold
-whatever was last in @array! It's similar to the problem demonstrated in
-the following C program:
-
- #include <pwd.h>
- main() {
- struct passwd *getpwnam(), *rp, *dp;
- rp = getpwnam("root");
- dp = getpwnam("daemon");
-
- printf("daemon name is %s\nroot name is %s\n",
- dp->pw_name, rp->pw_name);
- }
-
-Which will print
-
- daemon name is daemon
- root name is daemon
-
-The problem is that both C<rp> and C<dp> are pointers to the same location
-in memory! In C, you'd have to remember to malloc() yourself some new
-memory. In Perl, you'll want to use the array constructor C<[]> or the
-hash constructor C<{}> instead. Here's the right way to do the preceding
-broken code fragments:
-
- for $i (1..10) {
- @array = somefunc($i);
- $AoA[$i] = [ @array ];
+ my @AoA
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $AoA[$i] = [ @array ];
}
The square brackets make a reference to a new array with a I<copy>
-of what's in @array at the time of the assignment. This is what
-you want.
+of what's in C<@array>.
Note that this will produce something similar, but it's
much harder to read:
- for $i (1..10) {
- @array = 0 .. $i;
- @{$AoA[$i]} = @array;
+ my @AoA;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ @{ $AoA[$i] } = @array;
}
Is it the same? Well, maybe so--and maybe not. The subtle difference
is that when you assign something in square brackets, you know for sure
it's always a brand new reference with a new I<copy> of the data.
-Something else could be going on in this new case with the C<@{$AoA[$i]}}>
+Something else could be going on in this new case with the C<@{ $AoA[$i]} }>
dereference on the left-hand-side of the assignment. It all depends on
whether C<$AoA[$i]> had been undefined to start with, or whether it
already contained a reference. If you had already populated @AoA with
@@ -206,7 +177,7 @@
Then the assignment with the indirection on the left-hand-side would
use the existing reference that was already there:
- @{$AoA[3]} = @array;
+ @{ $AoA[3] } = @array;
Of course, this I<would> have the "interesting" effect of clobbering
@another_array. (Have you ever noticed how when a programmer says
@@ -221,9 +192,10 @@
Surprisingly, the following dangerous-looking construct will
actually work out fine:
- for $i (1..10) {
- my @array = somefunc($i);
- $AoA[$i] = \@array;
+ my @AoA;
+ for my $i (1..10) {
+ my @array = somefunc($i);
+ $AoA[$i] = \@array;
}
That's because my() is more of a run-time statement than it is a
@@ -242,14 +214,14 @@
In summary:
- $AoA[$i] = [ @array ]; # usually best
- $AoA[$i] = \@array; # perilous; just how my() was that array?
- @{ $AoA[$i] } = @array; # way too tricky for most programmers
+ $AoA[$i] = [ @array ]; # usually best
+ $AoA[$i] = \@array; # perilous; just how my() is that array?
+ @{ $AoA[$i] } = @array; # way too tricky for most programmers
=head1 CAVEAT ON PRECEDENCE
-Speaking of things like C<@{$AoA[$i]}>, the following are actually the
+Speaking of things like C<@{ $AoA[$i] }>, the following are actually the
same thing:
$aref->[2][2] # clear
@@ -284,9 +256,9 @@
this:
my $aref = [
- [ "fred", "barney", "pebbles", "bambam", "dino", ],
- [ "homer", "bart", "marge", "maggie", ],
- [ "george", "jane", "elroy", "judy", ],
+ [ 'fred', 'barney', 'pebbles', 'bambam', 'dino', ],
+ [ 'homer', 'bart', 'marge', 'maggie', ],
+ [ 'george', 'jane', 'elroy', 'judy', ],
];
print $aref[2][2];
@@ -334,55 +306,60 @@
=head2 Declaration of a ARRAY OF ARRAYS
- @AoA = (
- [ "fred", "barney" ],
- [ "george", "jane", "elroy" ],
- [ "homer", "marge", "bart" ],
+ my @AoA = (
+ [ 'fred', 'barney' ],
+ [ 'george', 'jane', 'elroy' ],
+ [ 'homer', 'marge', 'bart' ],
);
=head2 Generation of a ARRAY OF ARRAYS
# reading from file
+ my @AoA;
while ( <> ) {
push @AoA, [ split ];
}
# calling a function
- for $i ( 1 .. 10 ) {
+ my @AoA;
+ foreach my $i ( 1 .. 10 ) {
$AoA[$i] = [ somefunc($i) ];
}
# using temp vars
- for $i ( 1 .. 10 ) {
- @tmp = somefunc($i);
- $AoA[$i] = [ @tmp ];
+ my @AoA;
+ foreach my $i ( 1 .. 10 ) {
+ my @tmp = somefunc($i);
+ $AoA[$i] = [ @tmp ];
}
# add to an existing row
- push @{ $AoA[0] }, "wilma", "betty";
+ push @{ $AoA[0] }, 'wilma', 'betty';
=head2 Access and Printing of a ARRAY OF ARRAYS
+ my @AoA;
+
# one element
- $AoA[0][0] = "Fred";
+ $AoA[0][0] = 'Fred';
# another element
$AoA[1][1] =~ s/(\w)/\u$1/;
# print the whole thing with refs
- for $aref ( @AoA ) {
+ foreach my $aref ( @AoA ) {
print "\t [ @$aref ],\n";
}
# print the whole thing with indices
- for $i ( 0 .. $#AoA ) {
- print "\t [ @{$AoA[$i]} ],\n";
+ foreach my $i ( 0 .. $#AoA ) {
+ print "\t [ @{ $AoA[$i] } ],\n";
}
# print the whole thing one at a time
- for $i ( 0 .. $#AoA ) {
- for $j ( 0 .. $#{ $AoA[$i] } ) {
- print "elt $i $j is $AoA[$i][$j]\n";
+ foreach my $i ( 0 .. $#AoA ) {
+ foreach my $j ( 0 .. $#{ $AoA[$i] } ) {
+ print "element $i $j is $AoA[$i][$j]\n";
}
}
@@ -390,77 +367,86 @@
=head2 Declaration of a HASH OF ARRAYS
- %HoA = (
- flintstones => [ "fred", "barney" ],
- jetsons => [ "george", "jane", "elroy" ],
- simpsons => [ "homer", "marge", "bart" ],
+ my %HoA = (
+ flintstones => [ 'fred', 'barney' ],
+ jetsons => [ 'george', 'jane', 'elroy' ],
+ simpsons => [ 'homer', 'marge', 'bart' ],
);
=head2 Generation of a HASH OF ARRAYS
# reading from file
# flintstones: fred barney wilma dino
+ my %HoA;
while ( <> ) {
- next unless s/^(.*?):\s*//;
+ next unless s/^([^:]*):\s*//;
$HoA{$1} = [ split ];
}
# reading from file; more temps
# flintstones: fred barney wilma dino
- while ( $line = <> ) {
- ($who, $rest) = split /:\s*/, $line, 2;
- @fields = split ' ', $rest;
- $HoA{$who} = [ @fields ];
+ my %HoA;
+ while ( my $line = <> ) {
+ my ($who, $rest) = split /:\s*/, $line, 2;
+ my @fields = split ' ', $rest;
+ $HoA{$who} = [ @fields ];
}
# calling a function that returns a list
- for $group ( "simpsons", "jetsons", "flintstones" ) {
+ my %HoA;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
$HoA{$group} = [ get_family($group) ];
}
# likewise, but using temps
- for $group ( "simpsons", "jetsons", "flintstones" ) {
- @members = get_family($group);
- $HoA{$group} = [ @members ];
+ my %HoA;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
+ my @members = get_family($group);
+ $HoA{$group} = [ @members ];
}
# append new members to an existing family
- push @{ $HoA{"flintstones"} }, "wilma", "betty";
+ push @{ $HoA{flintstones} }, 'wilma', 'betty';
=head2 Access and Printing of a HASH OF ARRAYS
+ my %HoA;
+
# one element
- $HoA{flintstones}[0] = "Fred";
+ $HoA{flintstones}[0] = 'Fred';
# another element
$HoA{simpsons}[1] =~ s/(\w)/\u$1/;
# print the whole thing
- foreach $family ( keys %HoA ) {
- print "$family: @{ $HoA{$family} }\n"
+ foreach my $family ( keys %HoA ) {
+ print "$family: @{ $HoA{$family} }\n";
}
# print the whole thing with indices
- foreach $family ( keys %HoA ) {
- print "family: ";
- foreach $i ( 0 .. $#{ $HoA{$family} } ) {
+ foreach my $family ( keys %HoA ) {
+ print 'family: ';
+ foreach my $i ( 0 .. $#{ $HoA{$family} } ) {
print " $i = $HoA{$family}[$i]";
}
print "\n";
}
# print the whole thing sorted by number of members
- foreach $family ( sort { @{$HoA{$b}} <=> @{$HoA{$a}} } keys %HoA ) {
+ sub num_members {
+ @{ $HoA{$b} } <=> @{ $HoA{$a} }
+ }
+ foreach my $family ( sort num_members keys %HoA ) {
print "$family: @{ $HoA{$family} }\n"
}
# print the whole thing sorted by number of members and name
- foreach $family ( sort {
- @{$HoA{$b}} <=> @{$HoA{$a}}
- ||
- $a cmp $b
- } keys %HoA )
- {
+ sub members_and_name {
+ @{ $HoA{$b} } <=> @{ $HoA{$a} }
+ ||
+ $a cmp $b
+ }
+ foreach my $family ( sort members_and_name keys %HoA ) {
print "$family: ", join(", ", sort @{ $HoA{$family} }), "\n";
}
@@ -468,20 +454,20 @@
=head2 Declaration of a ARRAY OF HASHES
- @AoH = (
+ my @AoH = (
{
- Lead => "fred",
- Friend => "barney",
+ Lead => 'fred',
+ Friend => 'barney',
},
{
- Lead => "george",
- Wife => "jane",
- Son => "elroy",
+ Lead => 'george',
+ Wife => 'jane',
+ Son => 'elroy',
},
{
- Lead => "homer",
- Wife => "marge",
- Son => "bart",
+ Lead => 'homer',
+ Wife => 'marge',
+ Son => 'bart',
}
);
@@ -489,11 +475,12 @@
# reading from file
# format: LEAD=fred FRIEND=barney
+ my @AoH;
while ( <> ) {
- $rec = {};
- for $field ( split ) {
- ($key, $value) = split /=/, $field;
- $rec->{$key} = $value;
+ my $rec = {};
+ foreach my $field ( split ) {
+ my($key, $value) = split /=/, $field;
+ $rec->{$key} = $value;
}
push @AoH, $rec;
}
@@ -502,55 +489,60 @@
# reading from file
# format: LEAD=fred FRIEND=barney
# no temp
+ my @AoH;
while ( <> ) {
push @AoH, { split /[\s+=]/ };
}
# calling a function that returns a key/value pair list, like
- # "lead","fred","daughter","pebbles"
- while ( %fields = getnextpairset() ) {
+ # lead => 'fred', daughter => 'pebbles'
+ my @AoH;
+ while ( my %fields = getnextpairset() ) {
push @AoH, { %fields };
}
# likewise, but using no temp vars
+ my @AoH;
while (<>) {
push @AoH, { parsepairs($_) };
}
# add key/value to an element
- $AoH[0]{pet} = "dino";
+ $AoH[0]{pet} = 'dino';
$AoH[2]{pet} = "santa's little helper";
=head2 Access and Printing of a ARRAY OF HASHES
+ my @AoH;
+
# one element
- $AoH[0]{lead} = "fred";
+ $AoH[0]{lead} = 'fred';
# another element
$AoH[1]{lead} =~ s/(\w)/\u$1/;
# print the whole thing with refs
- for $href ( @AoH ) {
- print "{ ";
- for $role ( keys %$href ) {
- print "$role=$href->{$role} ";
+ foreach my $href ( @AoH ) {
+ print '{ ';
+ foreach my $role ( keys %$href ) {
+ print "$role = $href->{$role} ";
}
print "}\n";
}
# print the whole thing with indices
- for $i ( 0 .. $#AoH ) {
+ foreach my $i ( 0 .. $#AoH ) {
print "$i is { ";
- for $role ( keys %{ $AoH[$i] } ) {
- print "$role=$AoH[$i]{$role} ";
+ foreach my $role ( keys %{ $AoH[$i] } ) {
+ print "$role = $AoH[$i]{$role} ";
}
print "}\n";
}
# print the whole thing one at a time
- for $i ( 0 .. $#AoH ) {
- for $role ( keys %{ $AoH[$i] } ) {
- print "elt $i $role is $AoH[$i]{$role}\n";
+ foreach my $i ( 0 .. $#AoH ) {
+ foreach my $role ( keys %{ $AoH[$i] } ) {
+ print "element $i $role is $AoH[$i]{$role}\n";
}
}
@@ -558,20 +550,20 @@
=head2 Declaration of a HASH OF HASHES
- %HoH = (
+ my %HoH = (
flintstones => {
- lead => "fred",
- pal => "barney",
+ lead => 'fred',
+ pal => 'barney',
},
jetsons => {
- lead => "george",
- wife => "jane",
- "his boy" => "elroy",
+ lead => 'george',
+ wife => 'jane',
+ 'his boy' => 'elroy',
},
simpsons => {
- lead => "homer",
- wife => "marge",
- kid => "bart",
+ lead => 'homer',
+ wife => 'marge',
+ kid => 'bart',
},
);
@@ -579,94 +571,113 @@
# reading from file
# flintstones: lead=fred pal=barney wife=wilma pet=dino
+ my %HoH;
while ( <> ) {
- next unless s/^(.*?):\s*//;
- $who = $1;
- for $field ( split ) {
- ($key, $value) = split /=/, $field;
+ next unless s/^([^:]*):\s*//;
+ my $who = $1;
+ for my $field ( split ) {
+ my($key, $value) = split /=/, $field;
$HoH{$who}{$key} = $value;
}
# reading from file; more temps
+ my %HoH;
while ( <> ) {
- next unless s/^(.*?):\s*//;
- $who = $1;
- $rec = {};
+ next unless s/^([^:]*):\s*//;
+ my $who = $1;
+ my $rec = {};
$HoH{$who} = $rec;
- for $field ( split ) {
- ($key, $value) = split /=/, $field;
- $rec->{$key} = $value;
+ foreach my $field ( split ) {
+ my($key, $value) = split /=/, $field;
+ $rec->{$key} = $value;
}
}
# calling a function that returns a key,value hash
- for $group ( "simpsons", "jetsons", "flintstones" ) {
+ my %HoH;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
$HoH{$group} = { get_family($group) };
}
# likewise, but using temps
- for $group ( "simpsons", "jetsons", "flintstones" ) {
- %members = get_family($group);
+ my %HoH;
+ foreach my $group ( 'simpsons', 'jetsons', 'flintstones' ) {
+ my %members = get_family($group);
$HoH{$group} = { %members };
}
# append new members to an existing family
- %new_folks = (
- wife => "wilma",
- pet => "dino",
+ my %HoH;
+ my %new_folks = (
+ wife => 'wilma',
+ pet => 'dino',
);
- for $what (keys %new_folks) {
+ foreach my $what (keys %new_folks) {
$HoH{flintstones}{$what} = $new_folks{$what};
}
=head2 Access and Printing of a HASH OF HASHES
+ %HoH;
+
# one element
- $HoH{flintstones}{wife} = "wilma";
+ $HoH{flintstones}{wife} = 'wilma';
# another element
$HoH{simpsons}{lead} =~ s/(\w)/\u$1/;
# print the whole thing
- foreach $family ( keys %HoH ) {
+ foreach my $family ( keys %HoH ) {
print "$family: { ";
- for $role ( keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
# print the whole thing somewhat sorted
- foreach $family ( sort keys %HoH ) {
+ foreach my $family ( sort keys %HoH ) {
print "$family: { ";
- for $role ( sort keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( sort keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
-
# print the whole thing sorted by number of members
- foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$a}} } keys %HoH ) {
+ sub num_members {
+ keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} }
+ }
+ foreach my $family ( sort num_members keys %HoH ) {
print "$family: { ";
- for $role ( sort keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( sort keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
# establish a sort order (rank) for each role
- $i = 0;
- for ( qw(lead wife son daughter pal pet) ) { $rank{$_} = ++$i }
+ my %rank;
+ my $i = 0;
+ foreach ( qw(lead wife son daughter pal pet) ) {
+ $rank{$_} = ++$i;
+ }
# now print the whole thing sorted by number of members
- foreach $family ( sort { keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} } } keys %HoH ) {
+ sub num_members {
+ keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} }
+ }
+ sub rank {
+ $rank{$a} <=> $rank{$b}
+ }
+
+ foreach my $family ( sort num_members keys %HoH ) {
print "$family: { ";
# and print these according to rank order
- for $role ( sort { $rank{$a} <=> $rank{$b} } keys %{ $HoH{$family} } ) {
- print "$role=$HoH{$family}{$role} ";
+ foreach my $role ( sort rank keys %{ $HoH{$family} } ) {
+ print "$role = $HoH{$family}{$role} ";
}
print "}\n";
}
@@ -679,7 +690,7 @@
Here's a sample showing how to create and use a record whose fields are of
many different sorts:
- $rec = {
+ my $rec = {
TEXT => $string,
SEQUENCE => [ @old_values ],
LOOKUP => { %some_table },
@@ -690,14 +701,14 @@
print $rec->{TEXT};
- print $rec->{SEQUENCE}[0];
- $last = pop @ { $rec->{SEQUENCE} };
+ print $rec->{SEQUENCE}->[0];
+ my $last = pop @{ $rec->{SEQUENCE} };
- print $rec->{LOOKUP}{"key"};
- ($first_k, $first_v) = each %{ $rec->{LOOKUP} };
+ print $rec->{LOOKUP}->{key};
+ my($first_k, $first_v) = each %{ $rec->{LOOKUP} };
- $answer = $rec->{THATCODE}->($arg);
- $answer = $rec->{THISCODE}->($arg1, $arg2);
+ my $answer = $rec->{THATCODE}->($arg);
+ my $result = $rec->{THISCODE}->($arg1, $arg2);
# careful of extra block braces on fh ref
print { $rec->{HANDLE} } "a string\n";
@@ -708,55 +719,52 @@
=head2 Declaration of a HASH OF COMPLEX RECORDS
- %TV = (
+ my %TV = (
flintstones => {
- series => "flintstones",
+ series => 'flintstones',
nights => [ qw(monday thursday friday) ],
members => [
- { name => "fred", role => "lead", age => 36, },
- { name => "wilma", role => "wife", age => 31, },
- { name => "pebbles", role => "kid", age => 4, },
+ { name => 'fred', role => 'lead', age => 36, },
+ { name => 'wilma', role => 'wife', age => 31, },
+ { name => 'pebbles', role => 'kid', age => 4, },
],
},
jetsons => {
- series => "jetsons",
+ series => 'jetsons',
nights => [ qw(wednesday saturday) ],
members => [
- { name => "george", role => "lead", age => 41, },
- { name => "jane", role => "wife", age => 39, },
- { name => "elroy", role => "kid", age => 9, },
+ { name => 'george", role => 'lead', age => 41, },
+ { name => 'jane", role => 'wife', age => 39, },
+ { name => 'elroy", role => 'kid', age => 9, },
],
},
simpsons => {
- series => "simpsons",
+ series => 'simpsons',
nights => [ qw(monday) ],
members => [
- { name => "homer", role => "lead", age => 34, },
- { name => "marge", role => "wife", age => 37, },
- { name => "bart", role => "kid", age => 11, },
+ { name => 'homer', role => 'lead', age => 34, },
+ { name => 'marge', role => 'wife', age => 37, },
+ { name => 'bart', role => 'kid', age => 11, },
],
},
);
=head2 Generation of a HASH OF COMPLEX RECORDS
- # reading from file
- # this is most easily done by having the file itself be
- # in the raw data format as shown above. perl is happy
- # to parse complex data structures if declared as data, so
- # sometimes it's easiest to do that
-
- # here's a piece by piece build up
- $rec = {};
- $rec->{series} = "flintstones";
+Here's a piece by piece build up of a hash of complex records. We'll
+read in a file that has our data in it.
+
+ my %TV = ();
+ my $rec = {};
+ $rec->{series} = 'flintstones';
$rec->{nights} = [ find_days() ];
- @members = ();
+ my @members = ();
# assume this file in field=value syntax
- while (<>) {
- %fields = split /[\s=]+/;
+ while ( <> ) {
+ my %fields = split /[\s=]+/, $_;
push @members, { %fields };
}
$rec->{members} = [ @members ];
@@ -764,19 +772,18 @@
# now remember the whole thing
$TV{ $rec->{series} } = $rec;
- ###########################################################
- # now, you might want to make interesting extra fields that
- # include pointers back into the same data structure so if
- # change one piece, it changes everywhere, like for example
- # if you wanted a {kids} field that was a reference
- # to an array of the kids' records without having duplicate
- # records and thus update problems.
- ###########################################################
- foreach $family (keys %TV) {
- $rec = $TV{$family}; # temp pointer
- @kids = ();
- for $person ( @{ $rec->{members} } ) {
- if ($person->{role} =~ /kid|son|daughter/) {
+Now, you might want to make interesting extra fields that
+include pointers back into the same data structure so if
+change one piece, it changes everywhere, like for example
+if you wanted a 'kids' field that was a reference
+to an array of the kids' records without having duplicate
+records and thus update problems.
+
+ foreach my $family ( keys %TV ) {
+ my $rec = $TV{$family}; # $rec points to $TV{$family}
+ my @kids = ();
+ foreach my $person ( @{ $rec->{members} } ) {
+ if ( $person->{role} =~ /kid|son|daughter/ ) {
push @kids, $person;
}
}
@@ -784,30 +791,33 @@
$rec->{kids} = [ @kids ];
}
- # you copied the array, but the array itself contains pointers
- # to uncopied objects. this means that if you make bart get
- # older via
+You copied the array, but the array itself contains pointers
+to uncopied objects. This means that if you make bart get
+older via
$TV{simpsons}{kids}[0]{age}++;
- # then this would also change in
- print $TV{simpsons}{members}[2]{age};
-
- # because $TV{simpsons}{kids}[0] and $TV{simpsons}{members}[2]
- # both point to the same underlying anonymous hash table
+Then this would also change in C<$TV{simpsons}{members}[2]{age}>
+because C<$TV{simpsons}{kids}[0]> and C<$TV{simpsons}{members}[2]>
+both point to the same underlying anonymous hash table.
# print the whole thing
- foreach $family ( keys %TV ) {
- print "the $family";
- print " is on during @{ $TV{$family}{nights} }\n";
- print "its members are:\n";
- for $who ( @{ $TV{$family}{members} } ) {
+ foreach my $family ( keys %TV ) {
+ print "the $family is on during @{ $TV{$family}{nights} }\n",
+ "its members are:\n";
+
+ foraech my $who ( @{ $TV{$family}{members} } ) {
print " $who->{name} ($who->{role}), age $who->{age}\n";
}
- print "it turns out that $TV{$family}{lead} has ";
- print scalar ( @{ $TV{$family}{kids} } ), " kids named ";
- print join (", ", map { $_->{name} } @{ $TV{$family}{kids} } );
- print "\n";
+
+ print "it turns out that $TV{$family}{lead} has ",
+ scalar ( @{ $TV{$family}{kids} } ),
+ ' kids named ',
+ join(
+ ', ',
+ map { $_->{name} } @{ $TV{$family}{kids} }
+ ),
+ "\n";
}
=head1 Database Ties
@@ -828,5 +838,8 @@
Tom Christiansen <F<[EMAIL PROTECTED]>>
-Last update:
+Last update (by Tom):
Wed Oct 23 04:57:50 MET DST 1996
+
+Last update (by Casey West, <F<[EMAIL PROTECTED]>>
+Mon Sep 17 13:33:41 EDT 2001
