release 0.2 (tested)
Monday, 2 October 1995
$rec = {
STRING => $string,
LIST => [ @old_values ],
LOOKUP => { %some_table },
FUNC => \&some_function,
FANON => sub { $_[0] ** $_[1] },
FH => \*STDOUT,
};
print $rec->{STRING};
print $rec->{LIST}[0];
$last = pop @ { $rec->{LIST} };
print $rec->{LOOKUP}{"key"};
($first_k, $first_v) = each %{ $rec->{LOOKUP} };
$answer = &{ $rec->{FUNC} }($arg);
$answer = &{ $rec->{FANON} }($arg1, $arg2);
# careful of extra block braces on fh ref
print { $rec->{FH} } "a string\n";
use FileHandle;
$rec->{FH}->autoflush(1);
$rec->{FH}->print(" a string\n");
%TV = (
"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, },
],
},
"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, },
],
},
"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, },
],
},
);
# 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 datastructures if declared as data, so
# sometimes it's easiest to do that
# here's a piece by piece build up
$rec = {};
$rec->{series} = "flintstones";
$rec->{nights} = [ find_days() ];
@members = ();
# assume this file in field=value syntax
while () {
%fields = split /[\s=]+/;
push @members, { %fields };
}
$rec->{members} = [ @members ];
# 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 examples
# if you wanted a {kids} field that was an array reference
# to a list 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/) {
push @kids, $person;
}
}
# REMEMBER: $rec and $TV{$family} point to same data!!
$rec->{kids} = [ @kids ];
}
# you copied the list, but the list 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
# 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} } ) {
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";
}