Algorithm::Diff - Compute `intelligent' differences between two files / lists
require Algorithm::Diff;
# This example produces traditional 'diff' output:
my $diff = Algorithm::Diff->new( \@seq1, \@seq2 );
$diff->Base( 1 ); # Return line numbers, not indices
while( $diff->Next() ) {
next if $diff->Same();
my $sep = '';
if( ! $diff->Items(2) ) {
sprintf "%d,%dd%d\n",
$diff->Get(qw( Min1 Max1 Max2 ));
} elsif( ! $diff->Items(1) ) {
sprint "%da%d,%d\n",
$diff->Get(qw( Max1 Min2 Max2 ));
} else {
$sep = "---\n";
sprintf "%d,%dc%d,%d\n",
$diff->Get(qw( Min1 Max1 Min2 Max2 ));
}
print "< $_" for $diff->Items(1);
print $sep;
print "> $_" for $diff->Items(2);
}
# Alternate interfaces:
use Algorithm::Diff qw(
LCS LCS_length LCSidx
diff sdiff compact_diff
traverse_sequences traverse_balanced );
@lcs = LCS( \@seq1, \@seq2 );
$lcsref = LCS( \@seq1, \@seq2 );
$count = LCS_length( \@seq1, \@seq2 );
( $seq1idxref, $seq2idxref ) = LCSidx( \@seq1, \@seq2 );
# Complicated interfaces:
@diffs = diff( \@seq1, \@seq2 );
@sdiffs = sdiff( \@seq1, \@seq2 );
@cdiffs = compact_diff( \@seq1, \@seq2 );
traverse_sequences(
\@seq1,
\@seq2,
{ MATCH => \&callback1,
DISCARD_A => \&callback2,
DISCARD_B => \&callback3,
},
\&key_generator,
@extra_args,
);
traverse_balanced(
\@seq1,
\@seq2,
{ MATCH => \&callback1,
DISCARD_A => \&callback2,
DISCARD_B => \&callback3,
CHANGE => \&callback4,
},
\&key_generator,
@extra_args,
);
(by Mark-Jason Dominus)
I once read an article written by the authors of diff; they said
that they worked very hard on the algorithm until they found the
right one.
I think what they ended up using (and I hope someone will correct me, because I am not very confident about this) was the `longest common subsequence' method. In the LCS problem, you have two sequences of items:
a b c d f g h j q z
a b c d e f g i j k r x y z
and you want to find the longest sequence of items that is present in both original sequences in the same order. That is, you want to find a new sequence S which can be obtained from the first sequence by deleting some items, and from the secend sequence by deleting other items. You also want S to be as long as possible. In this case S is
a b c d f g j z
From there it's only a small step to get diff-like output:
e h i k q r x y
+ - + + - + + +
This module solves the LCS problem. It also includes a canned function
to generate diff-like output.
It might seem from the example above that the LCS of two sequences is always pretty obvious, but that's not always the case, especially when the two sequences have many repeated elements. For example, consider
a x b y c z p d q
a b c a x b y c z
A naive approach might start by matching up the a and b that
appear at the beginning of each sequence, like this:
a x b y c z p d q
a b c a b y c z
This finds the common subsequence a b c z. But actually, the LCS
is a x b y c z:
a x b y c z p d q
a b c a x b y c z
or
a x b y c z p d q
a b c a x b y c z
(See also the README file and several example scripts include with this module.)
This module now provides an object-oriented interface that uses less
memory and is easier to use than most of the previous procedural
interfaces. It also still provides several exportable functions. We'll
deal with these in ascending order of difficulty: LCS,
LCS_length, LCSidx, OO interface, prepare, diff, sdiff,
traverse_sequences, and traverse_balanced.
LCS
Given references to two lists of items, LCS returns an array containing their longest common subsequence. In scalar context, it returns a reference to such a list.
@lcs = LCS( \@seq1, \@seq2 );
$lcsref = LCS( \@seq1, \@seq2 );
LCS may be passed an optional third parameter; this is a CODE
reference to a key generation function. See /KEY GENERATION
FUNCTIONS.
@lcs = LCS( \@seq1, \@seq2, \&keyGen, @args );
$lcsref = LCS( \@seq1, \@seq2, \&keyGen, @args );
Additional parameters, if any, will be passed to the key generation routine.
LCS_length
This is just like LCS except it only returns the length of the
longest common subsequence. This provides a performance gain of about
9% compared to LCS.
LCSidx
Like LCS except it returns references to two arrays. The first array
contains the indices into @seq1 where the LCS items are located. The
second array contains the indices into @seq2 where the LCS items are located.
Therefore, the following three lists will contain the same values:
my( $idx1, $idx2 ) = LCSidx( \@seq1, \@seq2 );
my @list1 = @seq1[ @$idx1 ];
my @list2 = @seq2[ @$idx2 ];
my @list3 = LCS( \@seq1, \@seq2 );
new
$diff = Algorithm::Diffs->new( \@seq1, \@seq2 );
$diff = Algorithm::Diffs->new( \@seq1, \@seq2, \%opts );
new computes the smallest set of additions and deletions necessary
to turn the first sequence into the second and compactly records them
in the object.
You use the object to iterate over hunks, where each hunk represents a contiguous section of items which should be added, deleted, replaced, or left unchanged.
The following summary of all of the methods looks a lot like Perl code but some of the symbols have different meanings:
[ ] Encloses optional arguments
: Is followed by the default value for an optional argument
| Separates alternate return results
Method summary:
$obj = Algorithm::Diff->new( \@seq1, \@seq2, [ \%opts ] );
$pos = $obj->Next( [ $count : 1 ] );
$revPos = $obj->Prev( [ $count : 1 ] );
$obj = $obj->Reset( [ $pos : 0 ] );
$copy = $obj->Copy( [ $pos, [ $newBase ] ] );
$oldBase = $obj->Base( [ $newBase ] );
Note that all of the following methods die if used on an object that
is "reset" (not currently pointing at any hunk).
$bits = $obj->Diff( );
@items|$cnt = $obj->Same( );
@items|$cnt = $obj->Items( $seqNum );
@idxs |$cnt = $obj->Range( $seqNum, [ $base ] );
$minIdx = $obj->Min( $seqNum, [ $base ] );
$maxIdx = $obj->Max( $seqNum, [ $base ] );
@values = $obj->Get( @names );
Passing in undef for an optional argument is always treated the same
as if no argument were passed in.
Next
$pos = $diff->Next(); # Move forward 1 hunk
$pos = $diff->Next( 2 ); # Move forward 2 hunks
$pos = $diff->Next(-5); # Move backward 5 hunks
Next moves the object to point at the next hunk. The object starts
out "reset", which means it isn't pointing at any hunk. If the object
is reset, then Next() moves to the first hunk.
Next returns a true value iff the move didn't go past the last hunk.
So Next(0) will return true iff the object is not reset.
Actually, Next returns the object's new position, which is a number
between 1 and the number of hunks (inclusive), or returns a false value.
Prev
Prev($N) is almost identical to Next(-$N); it moves to the $Nth
previous hunk. On a 'reset' object, Prev() [and Next(-1)] move
to the last hunk.
The position returned by Prev is relative to the end of the
hunks; -1 for the last hunk, -2 for the second-to-last, etc.
Reset
$diff->Reset(); # Reset the object's position
$diff->Reset($pos); # Move to the specified hunk
$diff->Reset(1); # Move to the first hunk
$diff->Reset(-1); # Move to the last hunk
Reset returns the object, so, for example, you could use
$diff->Reset()->Next(-1) to get the number of hunks.
Copy
$copy = $diff->Copy( $newPos, $newBase );
Copy returns a copy of the object. The copy and the orignal object
share most of their data, so making copies takes very little memory.
The copy maintains its own position (separate from the original), which
is the main purpose of copies. It also maintains its own base.
By default, the copy's position starts out the same as the original
object's position. But Copy takes an optional first argument to set the
new position, so the following three snippets are equivalent:
$copy = $diff->Copy($pos);
$copy = $diff->Copy();
$copy->Reset($pos);
$copy = $diff->Copy()->Reset($pos);
Copy takes an optional second argument to set the base for
the copy. If you wish to change the base of the copy but leave
the position the same as in the original, here are two
equivalent ways:
$copy = $diff->Copy();
$copy->Base( 0 );
$copy = $diff->Copy(undef,0);
Here are two equivalent way to get a "reset" copy:
$copy = $diff->Copy(0);
$copy = $diff->Copy()->Reset();
Diff
$bits = $obj->Diff();
Diff returns a true value iff the current hunk contains items that are
different between the two sequences. It actually returns one of the
follow 4 values:
3==(1|2). This hunk contains items from @seq1 and the items
from @seq2 that should replace them. Both sequence 1 and 2
contain changed items so both the 1 and 2 bits are set.
Same
Same returns a true value iff the current hunk contains items that
are the same in both sequences. It actually returns the list of items
if they are the same or an emty list if they aren't. In a scalar
context, it returns the size of the list.
Items
$count = $diff->Items(2);
@items = $diff->Items($seqNum);
Items returns the (number of) items from the specified sequence that
are part of the current hunk.
If the current hunk contains only insertions, then
$diff->Items(1) will return an empty list (0 in a scalar conext).
If the current hunk contains only deletions, then $diff->Items(2)
will return an empty list (0 in a scalar conext).
If the hunk contains replacements, then both $diff->Items(1) and
$diff->Items(2) will return different, non-empty lists.
Otherwise, the hunk contains identical items and all of the following will return the same lists:
@items = $diff->Items(1);
@items = $diff->Items(2);
@items = $diff->Same();
Range
$count = $diff->Range( $seqNum );
@indices = $diff->Range( $seqNum );
@indices = $diff->Range( $seqNum, $base );
Range is like Items except that it returns a list of indices to
the items rather than the items themselves. By default, the index of
the first item (in each sequence) is 0 but this can be changed by
calling the Base method. So, by default, the following two snippets
return the same lists:
@list = $diff->Items(2);
@list = @seq2[ $diff->Range(2) ];
You can also specify the base to use as the second argument. So the following two snippets always return the same lists:
@list = $diff->Items(1);
@list = @seq1[ $diff->Range(1,0) ];
Base
$curBase = $diff->Base();
$oldBase = $diff->Base($newBase);
Base sets and/or returns the current base (usually 0 or 1) that is
used when you request range information. The base defaults to 0 so
that range information is returned as array indices. You can set the
base to 1 if you want to report traditional line numbers instead.
Min
$min1 = $diff->Min(1);
$min = $diff->Min( $seqNum, $base );
Min returns the first value that Range would return (given the
same arguments) or returns undef if Range would return an empty
list.
Max
Max returns the last value that Range would return or undef.
Get
( $n, $x, $r ) = $diff->Get(qw( min1 max1 range1 ));
@values = $diff->Get(qw( 0min2 1max2 range2 same base ));
Get returns one or more scalar values. You pass in a list of the
names of the values you want returned. Each name must match one of the
following regexes:
/^(-?\d+)?(min|max)[12]$/i
/^(range[12]|same|diff|base)$/i
The 1 or 2 after a name says which sequence you want the information for (and where allowed, it is required). The optional number before "min" or "max" is the base to use. So the following equalities hold:
$diff->Get('min1') == $diff->Min(1)
$diff->Get('0min2') == $diff->Min(2,0)
Using Get in a scalar context when you've passed in more than one
name is a fatal error (die is called).
prepare
Given a reference to a list of items, prepare returns a reference
to a hash which can be used when comparing this sequence to other
sequences with LCS or LCS_length.
$prep = prepare( \@seq1 );
for $i ( 0 .. 10_000 )
{
@lcs = LCS( $prep, $seq[$i] );
# do something useful with @lcs
}
prepare may be passed an optional third parameter; this is a CODE
reference to a key generation function. See /KEY GENERATION
FUNCTIONS.
$prep = prepare( \@seq1, \&keyGen );
for $i ( 0 .. 10_000 )
{
@lcs = LCS( $seq[$i], $prep, \&keyGen );
# do something useful with @lcs
}
Using prepare provides a performance gain of about 50% when calling LCS
many times compared with not preparing.
diff
@diffs = diff( \@seq1, \@seq2 );
$diffs_ref = diff( \@seq1, \@seq2 );
diff computes the smallest set of additions and deletions necessary
to turn the first sequence into the second, and returns a description
of these changes. The description is a list of hunks; each hunk
represents a contiguous section of items which should be added,
deleted, or replaced. (Hunks containing unchanged items are not
included.)
The return value of diff is a list of hunks, or, in scalar context, a
reference to such a list. If there are no differences, the list will be
empty.
Here is an example. Calling diff for the following two sequences:
a b c e h j l m n p
b c d e f j k l m r s t
would produce the following list:
(
[ [ '-', 0, 'a' ] ],
[ [ '+', 2, 'd' ] ],
[ [ '-', 4, 'h' ],
[ '+', 4, 'f' ] ],
[ [ '+', 6, 'k' ] ],
[ [ '-', 8, 'n' ],
[ '-', 9, 'p' ],
[ '+', 9, 'r' ],
[ '+', 10, 's' ],
[ '+', 11, 't' ] ],
)
There are five hunks here. The first hunk says that the a at
position 0 of the first sequence should be deleted (-). The second
hunk says that the d at position 2 of the second sequence should
be inserted (+). The third hunk says that the h at position 4
of the first sequence should be removed and replaced with the f
from position 4 of the second sequence. And so on.
diff may be passed an optional third parameter; this is a CODE
reference to a key generation function. See /KEY GENERATION
FUNCTIONS.
Additional parameters, if any, will be passed to the key generation routine.
sdiff
@sdiffs = sdiff( \@seq1, \@seq2 );
$sdiffs_ref = sdiff( \@seq1, \@seq2 );
sdiff computes all necessary components to show two sequences
and their minimized differences side by side, just like the
Unix-utility sdiff does:
same same
before | after
old < -
- > new
It returns a list of array refs, each pointing to an array of display instructions. In scalar context it returns a reference to such a list. If there are no differences, the list will have one entry per item, each indicating that the item was unchanged.
Display instructions consist of three elements: A modifier indicator
(+: Element added, -: Element removed, u: Element unmodified,
c: Element changed) and the value of the old and new elements, to
be displayed side-by-side.
An sdiff of the following two sequences:
a b c e h j l m n p
b c d e f j k l m r s t
results in
( [ '-', 'a', '' ],
[ 'u', 'b', 'b' ],
[ 'u', 'c', 'c' ],
[ '+', '', 'd' ],
[ 'u', 'e', 'e' ],
[ 'c', 'h', 'f' ],
[ 'u', 'j', 'j' ],
[ '+', '', 'k' ],
[ 'u', 'l', 'l' ],
[ 'u', 'm', 'm' ],
[ 'c', 'n', 'r' ],
[ 'c', 'p', 's' ],
[ '+', '', 't' ],
)
sdiff may be passed an optional third parameter; this is a CODE
reference to a key generation function. See /KEY GENERATION
FUNCTIONS.
Additional parameters, if any, will be passed to the key generation routine.
compact_diff
compact_diff is much like sdiff except it returns a much more
compact description consisting of just one flat list of indices. An
example helps explain the format:
my @a = qw( a b c e h j l m n p );
my @b = qw( b c d e f j k l m r s t );
@cdiff = compact_diff( \@a, \@b );
# Returns:
# @a @b @a @b
# start start values values
( 0, 0, # =
0, 0, # a !
1, 0, # b c = b c
3, 2, # ! d
3, 3, # e = e
4, 4, # f ! h
5, 5, # j = j
6, 6, # ! k
6, 7, # l m = l m
8, 9, # n p ! r s t
10, 12, #
);
The 0th, 2nd, 4th, etc. entries are all indices into @seq1 (@a in the above example) indicating where a hunk begins. The 1st, 3rd, 5th, etc. entries are all indices into @seq2 (@b in the above example) indicating where the same hunk begins.
So each pair of indices (except the last pair) describes where a hunk begins (in each sequence). Since each hunk must end at the item just before the item that starts the next hunk, the next pair of indices can be used to determine where the hunk ends.
So, the first 4 entries (0..3) describe the first hunk. Entries 0 and 1
describe where the first hunk begins (and so are always both 0).
Entries 2 and 3 describe where the next hunk begins, so subtracting 1
from each tells us where the first hunk ends. That is, the first hunk
contains items $diff[0] through $diff[2] - 1 of the first sequence
and contains items $diff[1] through $diff[3] - 1 of the second
sequence.
In other words, the first hunk consists of the following two lists of items:
# 1st pair 2nd pair
# of indices of indices
@list1 = @a[ $cdiff[0] .. $cdiff[2]-1 ];
@list2 = @b[ $cdiff[1] .. $cdiff[3]-1 ];
# Hunk start Hunk end
Note that the hunks will always alternate between those that are part of the LCS (those that contain unchanged items) and those that contain changes. This means that all we need to be told is whether the first hunk is a 'same' or 'diff' hunk and we can determine which of the other hunks contain 'same' items or 'diff' items.
By convention, we always make the first hunk contain unchanged items. So the 1st, 3rd, 5th, etc. hunks (all odd-numbered hunks if you start counting from 1) all contain unchanged items. And the 2nd, 4th, 6th, etc. hunks (all even-numbered hunks if you start counting from 1) all contain changed items.
Since @a and @b don't begin with the same value, the first hunk in our example is empty (otherwise we'd violate the above convention). Note that the first 4 index values in our example are all zero. Plug these values into our previous code block and we get:
@hunk1a = @a[ 0 .. 0-1 ];
@hunk1b = @b[ 0 .. 0-1 ];
And 0..-1 returns the empty list.
Move down one pair of indices (2..5) and we get the offset ranges for the second hunk, which contains changed items.
Since @diff[2..5] contains (0,0,1,0) in our example, the second hunk
consists of these two lists of items:
@hunk2a = @a[ $cdiff[2] .. $cdiff[4]-1 ];
@hunk2b = @b[ $cdiff[3] .. $cdiff[5]-1 ];
# or
@hunk2a = @a[ 0 .. 1-1 ];
@hunk2b = @b[ 0 .. 0-1 ];
# or
@hunk2a = @a[ 0 .. 0 ];
@hunk2b = @b[ 0 .. -1 ];
# or
@hunk2a = ( 'a' );
@hunk2b = ( );
That is, we would delete item 0 ('a') from @a.
Since @diff[4..7] contains (1,0,3,2) in our example, the third hunk
consists of these two lists of items:
@hunk3a = @a[ $cdiff[4] .. $cdiff[6]-1 ];
@hunk3a = @b[ $cdiff[5] .. $cdiff[7]-1 ];
# or
@hunk3a = @a[ 1 .. 3-1 ];
@hunk3a = @b[ 0 .. 2-1 ];
# or
@hunk3a = @a[ 1 .. 2 ];
@hunk3a = @b[ 0 .. 1 ];
# or
@hunk3a = qw( b c );
@hunk3a = qw( b c );
Note that this third hunk contains unchanged items as our convention demands.
You can continue this process until you reach the last two indices, which will always be the number of items in each sequence. This is required so that subtracting one from each will give you the indices to the last items in each sequence.
traverse_sequences
traverse_sequences used to be the most general facility provided by
this module (the new OO interface is more powerful and much easier to
use).
Imagine that there are two arrows. Arrow A points to an element of
sequence A, and arrow B points to an element of the sequence B.
Initially, the arrows point to the first elements of the respective
sequences. traverse_sequences will advance the arrows through the
sequences one element at a time, calling an appropriate user-specified
callback function before each advance. It willadvance the arrows in
such a way that if there are equal elements $A[$i] and $B[$j]
which are equal and which are part of the LCS, there will be some moment
during the execution of traverse_sequences when arrow A is pointing
to $A[$i] and arrow B is pointing to $B[$j]. When this happens,
traverse_sequences will call the MATCH callback function and then
it will advance both arrows.
Otherwise, one of the arrows is pointing to an element of its sequence
that is not part of the LCS. traverse_sequences will advance that
arrow and will call the DISCARD_A or the DISCARD_B callback,
depending on which arrow it advanced. If both arrows point to elements
that are not part of the LCS, then traverse_sequences will advance
one of them and call the appropriate callback, but it is not specified
which it will call.
The arguments to traverse_sequences are the two sequences to
traverse, and a hash which specifies the callback functions, like this:
traverse_sequences(
\@seq1, \@seq2,
{ MATCH => $callback_1,
DISCARD_A => $callback_2,
DISCARD_B => $callback_3,
}
);
Callbacks for MATCH, DISCARD_A, and DISCARD_B are invoked with at least the indices of the two arrows as their arguments. They are not expected to return any values. If a callback is omitted from the table, it is not called.
Callbacks for A_FINISHED and B_FINISHED are invoked with at least the corresponding index in A or B.
If arrow A reaches the end of its sequence, before arrow B does,
traverse_sequences will call the A_FINISHED callback when it
advances arrow B, if there is such a function; if not it will call
DISCARD_B instead. Similarly if arrow B finishes first.
traverse_sequences returns when both arrows are at the ends of their
respective sequences. It returns true on success and false on failure.
At present there is no way to fail.
traverse_sequences may be passed an optional fourth parameter; this
is a CODE reference to a key generation function. See /KEY GENERATION
FUNCTIONS.
Additional parameters, if any, will be passed to the key generation function.
If you want to pass additional parameters to your callbacks, but don't need a custom key generation function, you can get the default by passing undef:
traverse_sequences(
\@seq1, \@seq2,
{ MATCH => $callback_1,
DISCARD_A => $callback_2,
DISCARD_B => $callback_3,
},
undef, # default key-gen
$myArgument1,
$myArgument2,
$myArgument3,
);
traverse_sequences does not have a useful return value; you are
expected to plug in the appropriate behavior with the callback
functions.
traverse_balanced
traverse_balanced is an alternative to traverse_sequences. It
uses a different algorithm to iterate through the entries in the
computed LCS. Instead of sticking to one side and showing element changes
as insertions and deletions only, it will jump back and forth between
the two sequences and report changes occurring as deletions on one
side followed immediatly by an insertion on the other side.
In addition to the DISCARD_A, DISCARD_B, and MATCH callbacks
supported by traverse_sequences, traverse_balanced supports
a CHANGE callback indicating that one element got replaced by another:
traverse_balanced(
\@seq1, \@seq2,
{ MATCH => $callback_1,
DISCARD_A => $callback_2,
DISCARD_B => $callback_3,
CHANGE => $callback_4,
}
);
If no CHANGE callback is specified, traverse_balanced
will map CHANGE events to DISCARD_A and DISCARD_B actions,
therefore resulting in a similar behaviour as traverse_sequences
with different order of events.
traverse_balanced might be a bit slower than traverse_sequences,
noticable only while processing huge amounts of data.
The sdiff function of this module
is implemented as call to traverse_balanced.
traverse_balanced does not have a useful return value; you are expected to
plug in the appropriate behavior with the callback functions.
Most of the functions accept an optional extra parameter. This is a CODE reference to a key generating (hashing) function that should return a string that uniquely identifies a given element. It should be the case that if two elements are to be considered equal, their keys should be the same (and the other way around). If no key generation function is provided, the key will be the element as a string.
By default, comparisons will use "eq" and elements will be turned into keys using the default stringizing operator '""'.
Where this is important is when you're comparing something other than strings. If it is the case that you have multiple different objects that should be considered to be equal, you should supply a key generation function. Otherwise, you have to make sure that your arrays contain unique references.
For instance, consider this example:
package Person;
sub new
{
my $package = shift;
return bless { name => '', ssn => '', @_ }, $package;
}
sub clone
{
my $old = shift;
my $new = bless { %$old }, ref($old);
}
sub hash
{
return shift()->{'ssn'};
}
my $person1 = Person->new( name => 'Joe', ssn => '123-45-6789' );
my $person2 = Person->new( name => 'Mary', ssn => '123-47-0000' );
my $person3 = Person->new( name => 'Pete', ssn => '999-45-2222' );
my $person4 = Person->new( name => 'Peggy', ssn => '123-45-9999' );
my $person5 = Person->new( name => 'Frank', ssn => '000-45-9999' );
If you did this:
my $array1 = [ $person1, $person2, $person4 ];
my $array2 = [ $person1, $person3, $person4, $person5 ];
Algorithm::Diff::diff( $array1, $array2 );
everything would work out OK (each of the objects would be converted into a string like "Person=HASH(0x82425b0)" for comparison).
But if you did this:
my $array1 = [ $person1, $person2, $person4 ];
my $array2 = [ $person1, $person3, $person4->clone(), $person5 ];
Algorithm::Diff::diff( $array1, $array2 );
$person4 and $person4->clone() (which have the same name and SSN) would be seen as different objects. If you wanted them to be considered equivalent, you would have to pass in a key generation function:
my $array1 = [ $person1, $person2, $person4 ];
my $array2 = [ $person1, $person3, $person4->clone(), $person5 ];
Algorithm::Diff::diff( $array1, $array2, \&Person::hash );
This would use the 'ssn' field in each Person as a comparison key, and so would consider $person4 and $person4->clone() as equal.
You may also pass additional parameters to the key generation function if you wish.
If you pass these routines a non-reference and they expect a reference, they will die with a message.
This version released by Tye McQueen (http://perlmonks.org/?node=tye).
Parts Copyright (c) 2000-2004 Ned Konz. All rights reserved. Parts by Tye McQueen.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl.
Mark-Jason still maintains a mailing list. To join a low-volume mailing list for announcements related to diff and Algorithm::Diff, send an empty mail message to mjd-perl-diff-request@plover.com.
Versions through 0.59 (and much of this documentation) were written by:
Mark-Jason Dominus, mjd-perl-diff@plover.com
This version borrows some documentation and routine names from Mark-Jason's, but Diff.pm's code was completely replaced.
This code was adapted from the Smalltalk code of Mario Wolczko <mario@wolczko.com>, which is available at ftp://st.cs.uiuc.edu/pub/Smalltalk/MANCHESTER/manchester/4.0/diff.st
sdiff and traverse_balanced were written by Mike Schilli
<m@perlmeister.com>.
The algorithm is that described in A Fast Algorithm for Computing Longest Common Subsequences, CACM, vol.20, no.5, pp.350-353, May 1977, with a few minor improvements to improve the speed.
Much work was done by Ned Konz (perl@bike-nomad.com).
The OO interface and some other changes are by Tye McQueen.