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.\" ========================================================================
.\"
.IX Title "Algorithm::DiffOld 3pm"
.TH Algorithm::DiffOld 3pm "2018-08-25" "perl v5.26.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
Algorithm::DiffOld \- Compute `intelligent' differences between two files / lists
but use the old (<=0.59) interface.
.SH "NOTE"
.IX Header "NOTE"
This has been provided as part of the Algorithm::Diff package by Ned Konz.
This particular module is \fB\s-1ONLY\s0\fR for people who \fB\s-1HAVE\s0\fR to have the old
interface, which uses a comparison function rather than a key generating
function.
.PP
Because each of the lines in one array have to be compared with each 
of the lines in the other array, this does M*N comparisons. This can
be very slow. I clocked it at taking 18 times as long as the stock
version of Algorithm::Diff for a 4000\-line file. It will get worse
quadratically as array sizes increase.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use Algorithm::DiffOld qw(diff LCS traverse_sequences);
\&
\&  @lcs    = LCS( \e@seq1, \e@seq2, $comparison_function );
\&
\&  $lcsref = LCS( \e@seq1, \e@seq2, $comparison_function );
\&
\&  @diffs = diff( \e@seq1, \e@seq2, $comparison_function );
\&  
\&  traverse_sequences( \e@seq1, \e@seq2,
\&                     { MATCH => $callback,
\&                       DISCARD_A => $callback,
\&                       DISCARD_B => $callback,
\&                     },
\&                     $comparison_function );
.Ve
.SH "COMPARISON FUNCTIONS"
.IX Header "COMPARISON FUNCTIONS"
Each of the main routines should be passed a comparison function. If you
aren't passing one in, \fBuse Algorithm::Diff instead\fR.
.PP
These functions should return a true value when two items should compare
as equal.
.PP
For instance,
.PP
.Vb 1
\&  @lcs    = LCS( \e@seq1, \e@seq2, sub { my ($a, $b) = @_; $a eq $b } );
.Ve
.PP
but if that is all you're doing with your comparison function, just use
Algorithm::Diff and let it do this (this is its default).
.PP
Or:
.PP
.Vb 5
\&  sub someFunkyComparisonFunction
\&  {
\&        my ($a, $b) = @_;
\&        $a =~ m{$b};
\&  }
\&
\&  @diffs = diff( \e@lines, \e@patterns, \e&someFunkyComparisonFunction );
.Ve
.PP
which would allow you to diff an array \f(CW@lines\fR which consists of text
lines with an array \f(CW@patterns\fR which consists of regular expressions.
.PP
This is actually the reason I wrote this version \*(-- there is no way
to do this with a key generation function as in the stock Algorithm::Diff.