=head1 NAME
+X<data structure> X<complex data structure> X<struct>
perldsc - Perl Data Structures Cookbook
prior to its 5.0 release was complex data structures. Even without direct
language support, some valiant programmers did manage to emulate them, but
it was hard work and not for the faint of heart. You could occasionally
-get away with the C<$m{$
LoL,$b}> notation borrowed from I<awk> in which the
-keys are actually more like a single concatenated string C<"$LoL$b">, but
+get away with the C<$m{$
AoA,$b}> notation borrowed from B<awk> in which the
+keys are actually more like a single concatenated string C<"$AoA$b">, but
traversal and sorting were difficult. More desperate programmers even
hacked Perl's internal symbol table directly, a strategy that proved hard
to develop and maintain--to put it mildly.
The 5.0 release of Perl let us have complex data structures. You
-may now write something like this and all of a sudden, you'd have a array
+may now write something like this and all of a sudden, you'd have an array
with three dimensions!
for $x (1 .. 10) {
for $y (1 .. 10) {
for $z (1 .. 10) {
- $LoL[$x][$y][$z] =
+ $AoA[$x][$y][$z] =
$x ** $y + $z;
}
}
Alas, however simple this may appear, underneath it's a much more
elaborate construct than meets the eye!
-How do you print it out? Why can't you just say C<print @LoL>? How do
+How do you print it out? Why can't you say just C<print @AoA>? How do
you sort it? How can you pass it to a function or get one of these back
-from a function? Is is an object? Can you save it to disk to read
+from a function? Is it an object? Can you save it to disk to read
back later? How do you access whole rows or columns of that matrix? Do
all the values have to be numeric?
implementation, it's really more due to a lack of existing documentation with
examples designed for the beginner.
-This document is meant to be a detailed but understandable treatment of
-the many different sorts of data structures you might want to develop. It should
-also serve as a cookbook of examples. That way, when you need to create one of these
-complex data structures, you can just pinch, pilfer, or purloin
-a drop-in example from here.
+This document is meant to be a detailed but understandable treatment of the
+many different sorts of data structures you might want to develop. It
+should also serve as a cookbook of examples. That way, when you need to
+create one of these complex data structures, you can just pinch, pilfer, or
+purloin a drop-in example from here.
Let's look at each of these possible constructs in detail. There are separate
-documents on each of the following:
+sections on each of the following:
=over 5
=item * more elaborate constructs
-=item * recursive and self-referential data structures
-
-=item * objects
-
=back
-But for now, let's look at some of the general issues common to all
-of these types of data structures.
+But for now, let's look at general issues common to all
+these types of data structures.
=head1 REFERENCES
+X<reference> X<dereference> X<dereferencing> X<pointer>
-The most important thing to understand about all data structures in Perl
--- including multidimensional arrays--is that even though they might
+The most important thing to understand about all data structures in
+Perl--including multidimensional arrays--is that even though they might
appear otherwise, Perl C<@ARRAY>s and C<%HASH>es are all internally
-one-dimensional. They can only hold scalar values (meaning a string,
+one-dimensional. They can hold only scalar values (meaning a string,
number, or a reference). They cannot directly contain other arrays or
hashes, but instead contain I<references> to other arrays or hashes.
+X<multidimensional array> X<array, multidimensional>
-You can't use a reference to a array or hash in quite the same way that
-you would a real array or hash. For C or C++ programmers unused to distinguishing
-between arrays and pointers to the same, this can be confusing. If so,
-just think of it as the difference between a structure and a pointer to a
-structure.
+You can't use a reference to an array or hash in quite the same way that you
+would a real array or hash. For C or C++ programmers unused to
+distinguishing between arrays and pointers to the same, this can be
+confusing. If so, just think of it as the difference between a structure
+and a pointer to a structure.
-You can (and should) read more about references in the perlref(1) man
-page. Briefly, references are rather like pointers that know what they
+You can (and should) read more about references in L<perlref>.
+Briefly, references are rather like pointers that know what they
point to. (Objects are also a kind of reference, but we won't be needing
them right away--if ever.) This means that when you have something which
looks to you like an access to a two-or-more-dimensional array and/or hash,
two-dimensional one. This is actually the way almost all C
multidimensional arrays work as well.
- $list[7][12] # array of arrays
- $list[7]{string} # array of hashes
+ $array[7][12] # array of arrays
+ $array[7]{string} # array of hashes
$hash{string}[7] # hash of arrays
$hash{string}{'another string'} # hash of hashes
-Now, because the top level only contains references, if you try to print
+Now, because the top level contains only references, if you try to print
out your array in with a simple print() function, you'll get something
that doesn't look very nice, like this:
- @LoL = ( [2, 3], [4, 5, 7], [0] );
- print $LoL[1][2];
+ @AoA = ( [2, 3], [4, 5, 7], [0] );
+ print $AoA[1][2];
7
- print @LoL;
+ print @AoA;
ARRAY(0x83c38)ARRAY(0x8b194)ARRAY(0x8b1d0)
of a nested array:
for $i (1..10) {
- @list = somefunc($i);
- $LoL[$i] = @list; # WRONG!
+ @array = somefunc($i);
+ $AoA[$i] = @array; # WRONG!
}
-That's just the simple case of assigning a list to a scalar and getting
+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 $i (1..10) {
- @list = somefunc($i);
- $counts[$i] = scalar @list;
+ @array = somefunc($i);
+ $counts[$i] = scalar @array;
}
Here's the case of taking a reference to the same memory location
again and again:
for $i (1..10) {
- @list = somefunc($i);
- $LoL[$i] = \@list; # WRONG!
+ @array = somefunc($i);
+ $AoA[$i] = \@array; # WRONG!
}
-So, just what's the big problem with that? It looks right, doesn't it?
+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 @LoL refer to the I<very same place>, and they will therefore all hold
-whatever was last in @list! It's similar to the problem demonstrated in
+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>
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:
+X<[]> X<{}>
for $i (1..10) {
- @list = somefunc($i);
- $LoL[$i] = [ @list ];
+ @array = somefunc($i);
+ $AoA[$i] = [ @array ];
}
The square brackets make a reference to a new array with a I<copy>
-of what's in @list at the time of the assignment. This is what
+of what's in @array at the time of the assignment. This is what
you want.
Note that this will produce something similar, but it's
much harder to read:
for $i (1..10) {
- @list = 0 .. $i;
- @{$LoL[$i]} = @list;
+ @array = 0 .. $i;
+ @{$AoA[$i]} = @array;
}
Is it the same? Well, maybe so--and maybe not. The subtle difference
is that when you assign something in square brackets, you know for sure
it's always a brand new reference with a new I<copy> of the data.
-Something else could be going on in this new case with the C<@{$LoL[$i]}}>
+Something else could be going on in this new case with the C<@{$AoA[$i]}>
dereference on the left-hand-side of the assignment. It all depends on
-whether C<$LoL[$i]> had been undefined to start with, or whether it
-already contained a reference. If you had already populated @LoL with
+whether C<$AoA[$i]> had been undefined to start with, or whether it
+already contained a reference. If you had already populated @AoA with
references, as in
- $LoL[3] = \@another_list;
+ $AoA[3] = \@another_array;
Then the assignment with the indirection on the left-hand-side would
use the existing reference that was already there:
- @{$LoL[3]} = @list;
+ @{$AoA[3]} = @array;
Of course, this I<would> have the "interesting" effect of clobbering
-@another_list. (Have you ever noticed how when a programmer says
+@another_array. (Have you ever noticed how when a programmer says
something is "interesting", that rather than meaning "intriguing",
they're disturbingly more apt to mean that it's "annoying",
"difficult", or both? :-)
-So just remember to always use the array or hash constructors with C<[]>
+So just remember always to use the array or hash constructors with C<[]>
or C<{}>, and you'll be fine, although it's not always optimally
efficient.
actually work out fine:
for $i (1..10) {
- my @list = somefunc($i);
- $LoL[$i] = \@list;
+ my @array = somefunc($i);
+ $AoA[$i] = \@array;
}
That's because my() is more of a run-time statement than it is a
In summary:
- $LoL[$i] = [ @list ]; # usually best
- $LoL[$i] = \@list; # perilous; just how my() was that list?
- @{ $LoL[$i] } = @list; # way too tricky for most programmers
+ $AoA[$i] = [ @array ]; # usually best
+ $AoA[$i] = \@array; # perilous; just how my() was that array?
+ @{ $AoA[$i] } = @array; # way too tricky for most programmers
=head1 CAVEAT ON PRECEDENCE
+X<dereference, precedence> X<dereferencing, precedence>
-Speaking of things like C<@{$LoL[$i]}>, the following are actually the
+Speaking of things like C<@{$AoA[$i]}>, the following are actually the
same thing:
+X<< -> >>
- $listref->[2][2] # clear
- $$listref[2][2] # confusing
+ $aref->[2][2] # clear
+ $$aref[2][2] # confusing
That's because Perl's precedence rules on its five prefix dereferencers
(which look like someone swearing: C<$ @ * % &>) make them bind more
element of C<a>. That is, they first take the subscript, and only then
dereference the thing at that subscript. That's fine in C, but this isn't C.
-The seemingly equivalent construct in Perl, C<$$listref[$i]> first does
-the deref of C<$listref>, making it take $listref as a reference to an
+The seemingly equivalent construct in Perl, C<$$aref[$i]> first does
+the deref of $aref, making it take $aref as a reference to an
array, and then dereference that, and finally tell you the I<i'th> value
-of the array pointed to by $LoL. If you wanted the C notion, you'd have to
-write C<${$LoL[$i]}> to force the C<$LoL[$i]> to get evaluated first
+of the array pointed to by $AoA. If you wanted the C notion, you'd have to
+write C<${$AoA[$i]}> to force the C<$AoA[$i]> to get evaluated first
before the leading C<$> dereferencer.
=head1 WHY YOU SHOULD ALWAYS C<use strict>
also disallow accidental "symbolic dereferencing". Therefore if you'd done
this:
- my $listref = [
+ my $aref = [
[ "fred", "barney", "pebbles", "bambam", "dino", ],
[ "homer", "bart", "marge", "maggie", ],
- [ "george", "jane", "alroy", "judy", ],
+ [ "george", "jane", "elroy", "judy", ],
];
- print $listref[2][2];
+ print $aref[2][2];
The compiler would immediately flag that as an error I<at compile time>,
-because you were accidentally accessing C<@listref>, an undeclared
-variable, and it would thereby remind you to instead write:
+because you were accidentally accessing C<@aref>, an undeclared
+variable, and it would thereby remind you to write instead:
- print $listref->[2][2]
+ print $aref->[2][2]
=head1 DEBUGGING
+X<data structure, debugging> X<complex data structure, debugging>
+X<AoA, debugging> X<HoA, debugging> X<AoH, debugging> X<HoH, debugging>
+X<array of arrays, debugging> X<hash of arrays, debugging>
+X<array of hashes, debugging> X<hash of hashes, debugging>
-Before 5.002, the standard Perl debugger didn't do a very nice job of
-printing out complex data structures. With version 5.002 or above, the
+Before version 5.002, the standard Perl debugger didn't do a very nice job of
+printing out complex data structures. With 5.002 or above, the
debugger includes several new features, including command line editing as
well as the C<x> command to dump out complex data structures. For
-example, given the assignment to $LoL above, here's the debugger output:
+example, given the assignment to $AoA above, here's the debugger output:
- DB<1> X $LoL
- $LoL = ARRAY(0x13b5a0)
+ DB<1> x $AoA
+ $AoA = ARRAY(0x13b5a0)
0 ARRAY(0x1f0a24)
0 'fred'
1 'barney'
2 ARRAY(0x13b540)
0 'george'
1 'jane'
- 2 'alroy'
+ 2 'elroy'
3 'judy'
-There's also a lower-case B<x> command which is nearly the same.
-
=head1 CODE EXAMPLES
-Presented with little comment (these will get their own man pages someday)
+Presented with little comment (these will get their own manpages someday)
here are short code examples illustrating access of various
types of data structures.
-=head1 LISTS OF LISTS
+=head1 ARRAYS OF ARRAYS
+X<array of arrays> X<AoA>
-=head2 Declaration of a LIST OF LISTS
+=head2 Declaration of an ARRAY OF ARRAYS
- @LoL = (
+ @AoA = (
[ "fred", "barney" ],
[ "george", "jane", "elroy" ],
[ "homer", "marge", "bart" ],
);
-=head2 Generation of a LIST OF LISTS
+=head2 Generation of an ARRAY OF ARRAYS
# reading from file
while ( <> ) {
- push @LoL, [ split ];
+ push @AoA, [ split ];
}
# calling a function
for $i ( 1 .. 10 ) {
- $LoL[$i] = [ somefunc($i) ];
+ $AoA[$i] = [ somefunc($i) ];
}
# using temp vars
for $i ( 1 .. 10 ) {
@tmp = somefunc($i);
- $LoL[$i] = [ @tmp ];
+ $AoA[$i] = [ @tmp ];
}
# add to an existing row
- push @{ $LoL[0] }, "wilma", "betty";
+ push @{ $AoA[0] }, "wilma", "betty";
-=head2 Access and Printing of a LIST OF LISTS
+=head2 Access and Printing of an ARRAY OF ARRAYS
# one element
- $LoL[0][0] = "Fred";
+ $AoA[0][0] = "Fred";
# another element
- $LoL[1][1] =~ s/(\w)/\u$1/;
+ $AoA[1][1] =~ s/(\w)/\u$1/;
# print the whole thing with refs
- for $aref ( @LoL ) {
+ for $aref ( @AoA ) {
print "\t [ @$aref ],\n";
}
# print the whole thing with indices
- for $i ( 0 .. $#LoL ) {
- print "\t [ @{$LoL[$i]} ],\n";
+ for $i ( 0 .. $#AoA ) {
+ print "\t [ @{$AoA[$i]} ],\n";
}
# print the whole thing one at a time
- for $i ( 0 .. $#LoL ) {
- for $j ( 0 .. $#{$LoL[$i]} ) {
- print "elt $i $j is $LoL[$i][$j]\n";
+ for $i ( 0 .. $#AoA ) {
+ for $j ( 0 .. $#{ $AoA[$i] } ) {
+ print "elt $i $j is $AoA[$i][$j]\n";
}
}
-=head1 HASHES OF LISTS
+=head1 HASHES OF ARRAYS
+X<hash of arrays> X<HoA>
-=head2 Declaration of a HASH OF LISTS
+=head2 Declaration of a HASH OF ARRAYS
- %HoL = (
- "flintstones" => [ "fred", "barney" ],
- "jetsons" => [ "george", "jane", "elroy" ],
- "simpsons" => [ "homer", "marge", "bart" ],
+ %HoA = (
+ flintstones => [ "fred", "barney" ],
+ jetsons => [ "george", "jane", "elroy" ],
+ simpsons => [ "homer", "marge", "bart" ],
);
-=head2 Generation of a HASH OF LISTS
+=head2 Generation of a HASH OF ARRAYS
# reading from file
# flintstones: fred barney wilma dino
while ( <> ) {
next unless s/^(.*?):\s*//;
- $HoL{$1} = [ split ];
+ $HoA{$1} = [ split ];
}
# reading from file; more temps
while ( $line = <> ) {
($who, $rest) = split /:\s*/, $line, 2;
@fields = split ' ', $rest;
- $HoL{$who} = [ @fields ];
+ $HoA{$who} = [ @fields ];
}
# calling a function that returns a list
for $group ( "simpsons", "jetsons", "flintstones" ) {
- $HoL{$group} = [ get_family($group) ];
+ $HoA{$group} = [ get_family($group) ];
}
# likewise, but using temps
for $group ( "simpsons", "jetsons", "flintstones" ) {
@members = get_family($group);
- $HoL{$group} = [ @members ];
+ $HoA{$group} = [ @members ];
}
# append new members to an existing family
- push @{ $HoL{"flintstones"} }, "wilma", "betty";
+ push @{ $HoA{"flintstones"} }, "wilma", "betty";
-=head2 Access and Printing of a HASH OF LISTS
+=head2 Access and Printing of a HASH OF ARRAYS
# one element
- $HoL{flintstones}[0] = "Fred";
+ $HoA{flintstones}[0] = "Fred";
# another element
- $HoL{simpsons}[1] =~ s/(\w)/\u$1/;
+ $HoA{simpsons}[1] =~ s/(\w)/\u$1/;
# print the whole thing
- foreach $family ( keys %HoL ) {
- print "$family: @{ $HoL{$family} }\n"
+ foreach $family ( keys %HoA ) {
+ print "$family: @{ $HoA{$family} }\n"
}
# print the whole thing with indices
- foreach $family ( keys %HoL ) {
+ foreach $family ( keys %HoA ) {
print "family: ";
- foreach $i ( 0 .. $#{ $HoL{$family} ) {
- print " $i = $HoL{$family}[$i]";
+ foreach $i ( 0 .. $#{ $HoA{$family} } ) {
+ print " $i = $HoA{$family}[$i]";
}
print "\n";
}
# print the whole thing sorted by number of members
- foreach $family ( sort { @{$HoL{$b}} <=> @{$HoL{$b}} } keys %HoL ) {
- print "$family: @{ $HoL{$family} }\n"
+ foreach $family ( sort { @{$HoA{$b}} <=> @{$HoA{$a}} } keys %HoA ) {
+ print "$family: @{ $HoA{$family} }\n"
}
# print the whole thing sorted by number of members and name
- foreach $family ( sort { @{$HoL{$b}} <=> @{$HoL{$a}} } keys %HoL ) {
- print "$family: ", join(", ", sort @{ $HoL{$family}), "\n";
+ foreach $family ( sort {
+ @{$HoA{$b}} <=> @{$HoA{$a}}
+ ||
+ $a cmp $b
+ } keys %HoA )
+ {
+ print "$family: ", join(", ", sort @{ $HoA{$family} }), "\n";
}
-=head1 LISTS OF HASHES
+=head1 ARRAYS OF HASHES
+X<array of hashes> X<AoH>
-=head2 Declaration of a LIST OF HASHES
+=head2 Declaration of an ARRAY OF HASHES
- @LoH = (
+ @AoH = (
{
Lead => "fred",
Friend => "barney",
}
);
-=head2 Generation of a LIST OF HASHES
+=head2 Generation of an ARRAY OF HASHES
# reading from file
# format: LEAD=fred FRIEND=barney
($key, $value) = split /=/, $field;
$rec->{$key} = $value;
}
- push @LoH, $rec;
+ push @AoH, $rec;
}
# format: LEAD=fred FRIEND=barney
# no temp
while ( <> ) {
- push @LoH, { split /[\s+=]/ };
+ push @AoH, { split /[\s+=]/ };
}
- # calling a function that returns a key,value list, like
+ # calling a function that returns a key/value pair list, like
# "lead","fred","daughter","pebbles"
while ( %fields = getnextpairset() ) {
- push @LoH, { %fields };
+ push @AoH, { %fields };
}
# likewise, but using no temp vars
while (<>) {
- push @LoH, { parsepairs($_) };
+ push @AoH, { parsepairs($_) };
}
# add key/value to an element
- $LoH[0]{pet} = "dino";
- $LoH[2]{pet} = "santa's little helper";
+ $AoH[0]{pet} = "dino";
+ $AoH[2]{pet} = "santa's little helper";
-=head2 Access and Printing of a LIST OF HASHES
+=head2 Access and Printing of an ARRAY OF HASHES
# one element
- $LoH[0]{lead} = "fred";
+ $AoH[0]{lead} = "fred";
# another element
- $LoH[1]{lead} =~ s/(\w)/\u$1/;
+ $AoH[1]{lead} =~ s/(\w)/\u$1/;
# print the whole thing with refs
- for $href ( @LoH ) {
+ for $href ( @AoH ) {
print "{ ";
for $role ( keys %$href ) {
print "$role=$href->{$role} ";
}
# print the whole thing with indices
- for $i ( 0 .. $#LoH ) {
+ for $i ( 0 .. $#AoH ) {
print "$i is { ";
- for $role ( keys %{ $LoH[$i] } ) {
- print "$role=$LoH[$i]{$role} ";
+ for $role ( keys %{ $AoH[$i] } ) {
+ print "$role=$AoH[$i]{$role} ";
}
print "}\n";
}
# print the whole thing one at a time
- for $i ( 0 .. $#LoH ) {
- for $role ( keys %{ $LoH[$i] } ) {
- print "elt $i $role is $LoH[$i]{$role}\n";
+ for $i ( 0 .. $#AoH ) {
+ for $role ( keys %{ $AoH[$i] } ) {
+ print "elt $i $role is $AoH[$i]{$role}\n";
}
}
=head1 HASHES OF HASHES
+X<hash of hashes> X<HoH>
=head2 Declaration of a HASH OF HASHES
%HoH = (
- "flintstones" => {
- "lead" => "fred",
- "pal" => "barney",
+ flintstones => {
+ lead => "fred",
+ pal => "barney",
},
- "jetsons" => {
- "lead" => "george",
- "wife" => "jane",
- "his boy" => "elroy",
+ jetsons => {
+ lead => "george",
+ wife => "jane",
+ "his boy" => "elroy",
},
- "simpsons" => {
- "lead" => "homer",
- "wife" => "marge",
- "kid" => "bart",
+ simpsons => {
+ lead => "homer",
+ wife => "marge",
+ kid => "bart",
},
);
# append new members to an existing family
%new_folks = (
- "wife" => "wilma",
- "pet" => "dino";
+ wife => "wilma",
+ pet => "dino",
);
for $what (keys %new_folks) {
# print the whole thing sorted by number of members
- foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$b}} } keys %HoH ) {
+ foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$a}} } keys %HoH ) {
print "$family: { ";
for $role ( sort keys %{ $HoH{$family} } ) {
print "$role=$HoH{$family}{$role} ";
for ( 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{$b}} } keys %HoH ) {
+ foreach $family ( sort { keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} } } keys %HoH ) {
print "$family: { ";
# and print these according to rank order
- for $role ( sort { $rank{$a} <=> $rank{$b} keys %{ $HoH{$family} } } ) {
+ for $role ( sort { $rank{$a} <=> $rank{$b} } keys %{ $HoH{$family} } ) {
print "$role=$HoH{$family}{$role} ";
}
print "}\n";
=head1 MORE ELABORATE RECORDS
+X<record> X<structure> X<struct>
=head2 Declaration of MORE ELABORATE RECORDS
print $rec->{TEXT};
- print $rec->{LIST}[0];
+ print $rec->{SEQUENCE}[0];
$last = pop @ { $rec->{SEQUENCE} };
print $rec->{LOOKUP}{"key"};
($first_k, $first_v) = each %{ $rec->{LOOKUP} };
- $answer = &{ $rec->{THATCODE} }($arg);
- $answer = &{ $rec->{THISCODE} }($arg1, $arg2);
+ $answer = $rec->{THATCODE}->($arg);
+ $answer = $rec->{THISCODE}->($arg1, $arg2);
# careful of extra block braces on fh ref
print { $rec->{HANDLE} } "a string\n";
=head2 Declaration of a HASH OF COMPLEX RECORDS
%TV = (
- "flintstones" => {
+ flintstones => {
series => "flintstones",
nights => [ qw(monday thursday friday) ],
members => [
],
},
- "jetsons" => {
+ jetsons => {
series => "jetsons",
nights => [ qw(wednesday saturday) ],
members => [
],
},
- "simpsons" => {
+ simpsons => {
series => "simpsons",
nights => [ qw(monday) ],
members => [
# 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
+ # 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
###########################################################
# 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
+ # 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}} ) {
+ for $person ( @{ $rec->{members} } ) {
if ($person->{role} =~ /kid|son|daughter/) {
push @kids, $person;
}
$rec->{kids} = [ @kids ];
}
- # you copied the list, but the list itself contains pointers
+ # you copied the array, but the array itself contains pointers
# to uncopied objects. this means that if you make bart get
# older via
for $who ( @{ $TV{$family}{members} } ) {
print " $who->{name} ($who->{role}), age $who->{age}\n";
}
- print "it turns out that $TV{$family}{'lead'} has ";
+ 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";
hashes) to a dbm file. The first problem is that all but GDBM and
Berkeley DB have size limitations, but beyond that, you also have problems
with how references are to be represented on disk. One experimental
-module that does attempt to partially address this need is the MLDBM
-module. Check your nearest CPAN site as described in L<perlmod> for
+module that does partially attempt to address this need is the MLDBM
+module. Check your nearest CPAN site as described in L<perlmodlib> for
source code to MLDBM.
=head1 SEE ALSO
-perlref(1), perllol(1), perldata(1), perlobj(1)
+L<perlref>, L<perllol>, L<perldata>, L<perlobj>
=head1 AUTHOR
-Tom Christiansen E<lt>F<tchrist@perl.com>E<gt>
+Tom Christiansen <F<tchrist@perl.com>>
Last update:
-Mon Jul 8 05:22:49 MDT 1996
+Wed Oct 23 04:57:50 MET DST 1996
https://perl5.git.perl.org / perl5.git / blobdiff